PROCESS FOR RECOVERING HUM IC SUBSTANCES FROM PERCOLATE ORIGINATING FROM URBAN SOLID REFUSE DUMPS OR TH E LIKE, AN D HUMIC SUBSTANCE OBTAINED BY THE PROCESS

The present i nvention relates to a process for recovering h um ic substances from percolate originating from urban solid refuse dumps or the like, and a humic substance obtained by the process.

Hum ic substances are complex organic substances of variable and stil l not com pletely defined structure (su pramolecu lar, macromolecu lar structure), consisting of branched chains of mainly but not exclusively mono and polycyclic, including heterocyclic, aromatics with mainly carboxyl, phenol and hydroxyl functional groups, but also ethers, esters, amino, etc.

These substances are classified by their "solubil ity" (more precisely their capacity to form colloidal "sols") in water at various pHs (acid pH 0-7, neutral pH 7, basic pH 7-14) as indicated below:

- humic acids (HA) insoluble at acid pH and soluble at basic pH

- fulvic acids (FA) soluble at acid pH and at basic pH

- humines insoluble at acid pH and at basic pH

These sol u b il ity characteristics enable h u m ic su bstances to be extracted from carbonaceous minerals such as leonardite, lignite, peat and also, recently proposed, from compounds produced by transformation and stabil ization of organ ic refuse such as the organ ic fraction of sol id urban refuse (S.U.R) in controlled plants.

Leonardite, which forms in the slow decomposition of organic substances (in particular lignin) is the most recent surface oxidized phase of the geochemical transformation of vegetable organic substances in peat and lignite. It is particularly rich in humic substances, which are extracted in basic aqueous solution with potassium hydroxide (pH 9-12). These solutions, which can contain inorgan ic salts sol uble in basic water in variable q uantities, according to the zones of origin, are normally marketed, with various humic substance concentrations, in particular as soil improvers in agriculture. In this respect, humic substances modify the characteristics of soils and improve growth and health of the most varied agricultural crops both by soil treatment and by leaf application.

In particular, humic substances improve:

- soil water retention capacity;

- soil structure and fertility; by virtue of the chelating effect of the functional groups present in humic substances, the nutrients and microelements (iron, calcium, phosphorous, etc.) are prevented from being washed away and their availability is increased over time to the advantage of plant growth and health.

Hum ic substances are virtual ly non-biodegradable; they consist of macromol ecu l es of med iu m (FA) and h ig h mol ecu l ar weig ht (HA) with hydrophobic parts and hydrophilic functional groups which are partly acid, and in their sal ified forms with al kaline metals exhibit surfactant properties which enable them to be also used as surfactants in the washing of earth and soils for their decontam ination from hydrocarbons and/or heavy metals by also using their chelating properties on various heavy metals.

Substances similar to humic substances, but not of natural origin, have been obtained by controlled oxidation of coal and proposed as soil improvers or for inerting industrial ash rich in heavy metals.

It is known that, depend ing on the refuse qual ity and the degree of maturation of the dump and the rain level , the percolate from S.U .R. dumps can contain humic substance quantities (0.05-5 % by weight) considered interesting for industrial and commercial purposes; however their direct recovery from percolate by known methods does not enable a product to be obtained at competitive cost which is free from the various contaminants present in the percolate, with particular regard to nitrogenated and ammoniacal compounds, and consequently unsuitable for use similar to the humic substances obtained by previously described methods.

The object of the present invention is to provide a process enabling humic substances of marketable quality to be obtained from the percolate of S.U.R. dumps and similar refuse, while achieving lesser consumption of reagents (acids, additives) and using simple technologies, which can be integrated and used with existing technologies, to achieve low investment and running costs.

In attaining this object the following has to be considered.

The humic substance concentration in the percolate changes with the time (age) of activity of the S.U.R. dump; the succession of biological degradation stages which take place on the organic component of refuse once dumped are known to be the following:

- an initial short stage of aerobic biodegradation, principally due to interstitial oxygen, during which there is little production of percolate, or of humic substances;

- a second prolonged stage of anaerobic degradation, itself divided into the following successive stages:

a) acidogenic stage, in which volatile fatty acids and carbon dioxide form by fermentation, with consequent pH decrease. A large quantity of percolate forms with acid pH (5-6) having high BOD ₅ , high salt concentration, heavy metal mobilization but low humic substance presence;

b) acetogenic stage, in which volatile short chain acids form by fermentation, these being further degraded by acetogenic bacteria to acetic acid, a substrate of methanogenic bacteria. Methane is produced, hydrogen and carbon dioxide decrease and the pH increases. The percolate presents a lesser metal and BOD ₅ concentration than in the previous stage and an increase in humic substance and ammonia concentration;

c) methanogenic stage, in which methane is formed in large quantity by the prevalence of methanogenic, hydrogenophilic and above all acetophilic bacteria (responsible for the production of 70% of methane). This stage characterises the dump "maturity": the percolate presents neutral-alkaline pH (7-10); low volatile acid and dissolved solids concentrations (low BOD ₅ ), low mobility of heavy metals (for example Fe, Zn), high ammonia concentration, maximum humic substance concentration'

The percolate from a "mature" dump is in fact visually recognizable by its dark brown colour typical of humic substances (HA brown-black colour; FA yellow-brown colour). Studies conducted on the chemical and structural nature of humic substances obtained from the percolate of various S.U.R. dumps by chemico-physical analyses (spectroscopic, UV, FTIR, NMR, etc.) have shown that these are similar, but not equal, to those obtained by extraction from leonardite, peat, lignite, compost.

In purifying dump percolates, the humic substances are mainly removed together with the hydroxides and the basic carbonates of heavy metals by precipitation/clariflocculation with aluminium and iron salts, calcium hydroxide, organic flocculants, etc. implemented by technologies with membranes (ultrafiltration, reverse osmosis) which are however easily clogged by the humic substances. The sludges produced by the percolate purification are usually recycled to the dump or otherwise disposed of, it not being economically convenient to recover humic substances of sufficient commercial quality.

The "mature" percolate is already a basic humic substance solution and is normally classified, in accordance with Italian and European regulations, as "percolate refuse, special non-dangerous" (CER code 190703). A possible initial filtration is also provided to ensure that any "suspended solids" are at low level, less than 500 mg/litre, it being well known that certain dangerous organic m icrocontam inants, such as polychlorodibenzodioxins and polychlorodibenzofurans, if present, are practically absorbed into the insoluble particulate (suspended solids).

The object of the invention is to recover humic substances from this solution and to purify them of any contaminants present which render them unsuitable for each specific use.

In the present invention it has been found that if instead of treating the mature percolate at pH 7-10 with inorganic acid, for example sulphuric acid, until complete precipitation of the humic substances at pH 2-2.5, the same operation is carried out on the percolate after concentrating it from ten to twenty times by evaporation, for example under vacuum, it is sufficient to use an inorganic acid quantity equal to one quarter of that which would be used if the same quantity of non-concentrated percolate were treated. This reduction of about four times in the specific acid consumption is achieved by the sign ificant decrease in the percolate al kal in ity du ring the concentration procedure, because of the thermal decomposition of the bicarbonates and in particular of ammonium bicarbonate, typically present in high concentration in mature percolate, into ammonia and carbon dioxide, which are then removed from the percolate by evaporation.

Another advantage of operating the humic substance acid precipitation on the percolate concentrated by evaporation, for example under vacuum, is the virtually total absence in the concentrated percolate, and consequently in the humic substances precipitated from it, of possible volatile contaminants, either organic (carboxylic acids, hydrocarbons, other aliphatic/aromatic organic substances, includ ing halogenated and n itrogenated) or inorgan ic (pri ma ri ly am mon ia ); th is facil itates the su bseq u ent h u m ic su bsta nce purification stage to obtain humic substances of commercial quality.

Another advantage is that the stage of humic substance precipitation with acid can be carried out hot, at 50-100°C, at the temperature of the concentrated percolate d ischarge from the evaporator, without add itional energy costs, so improving the precipitate morphology and the efficiency of the subsequent stages of solid-liquid separation and purification by washing with water, possibly acidified with inorganic acid to pH <7 to reduce impurities such as inorganic salts and water-soluble organic compounds.

Another advantage of operating on the concentrated percolate is that during evaporation it undergoes thermal treatment with temperatures of 50- 1 30°C for a h ig h averag e res id ence ti me (2-7 hours) with consequent reduction of the initial bacterial load, which is also further reduced in the next stage of acidification to pH 2, obtaining a product virtually free of dangerous bacteria, such as Escherichia coli and salmonella. F i na l ly th e present i nvention , i n add ition to th e adva ntag eous economical implications (humic substances are a valuable product which, in addition to the current aforesaid uses, could find further profitable applications in the future) also has considerable environmental validity because it recovers from refuse a highly eco-compatible substance particularly useful for the recovery and improvement of arid and/or washed-out soils, favouring the conversion of carbon dioxide into vegetable biomass intended for food purposes or for the formation of renewable energy sources, with consequent reduction of emission of this greenhouse gas into the atmosphere.

This object is attained according to the invention by a process for recovering hum ic substances from percolate orig inating from urban sol id refuse dumps or the like as described in claim 1 .

A preferred embodiment of the present invention is further clarified hereinafter with reference to the accompanying block diagram and to some examples given by way of non-limiting example.

As can be seen from the block diagram, in the process according to the invention if the percolate originating from a S.U .R. dump or the l ike in its "maturation" phase conta ins suspended sol ids, it is in itial ly filtered with su itable filters such as sand filters, m icrofilters, decanters, centrifuges to obta i n a "su s pend ed sol id s" con centration of l ess th a n 500 mg/l itre (determined by the I RSA-CNR 2090 method) to remove any contaminant organic substances such as polychlorodibenzodioxins and polychlorodibenzofurans which, if present, are known to be adsorbed in the suspended solid particulate.

The particular percolate presents neutral or basic pH (pH 7-10), is brown in colour, contains more than 0.1 % of organic substances by weight determined as the difference between the dry residue at 1 05°C (R1 05) and the dry residue at 600°C (R600), determined by the IRSA Q64(2) 84 met.02 method , and i n particu lar more than 0.05% of h u m ic carbon by weig ht, determined by the DM 23-01 -91 S.O.G.U No. 29/91 method.

The percolate is then subjected to a continuous evaporation stage u nd e r vacu u m at a press u re of 5-200 KPa, temperature of 50-130°C, preferably by a continuous multiple effect process, for an average residence time of 2-7 hours, until a l iquid residue is obtained with a reduced volume equal to 1 /5 - 1 /29 of the initial percolate volume, at basic pH 8-1 1 .

The concentrated percolate contains all the humic substances in solution, in particular humic acids soluble in a basic environment, fulvic acids and inorganic salts, in particular chlorides, sulphates, phosphates, alkaline silicates (Na, K salts) and alkaline-earth silicates (Ca, Mg salts).

The condensate water of the evaporation-concentration stage contains al l the volati le contam inants present in the starting percolate, such as ammonia, volatile organic substances, hydrocarbons, halogenated organic substances. These substances are eliminated from the condensate water in a subsequent stripping/absorption stage wh ich also enables an ammon ium sulphate solution to be recovered, usable in industry. The condensate water purified in this manner can be used in the crude humic substance acid wash stage or d ischarged i nto the pu bl ic sewer, su rface waters or soi l , after possible further purification by known processes, for example oxidation , adsorption on active carbon, ultrafiltration, reverse osmosis, etc., to attain the contamination limits allowable for discharge.

The concentrated percolate is subjected to an acidification stage with the addition of an aqueous solution of organic acid, for example 37.5 wt% concentrated sulphuric acid, 37.5 wt% hydrochloric acid, 75 wt% phosphoric acid , at a tem peratu re between ambient and the boiling point of the concentrated percolate, under agitation, in a discontinuous or continuous precipitator, for example three-stage, with continuous line dispensing of acid, under pH control and under ag itation , for example by recycl ing with static mixers, until complete precipitation of a flocky humic substance solid at pH 1 - 3, preferably 2.0 stable (constant); the acid quantity required varies with the type of percolate and the type of acid : for example for a mature percolate, for 37.5 wt% sulphuric acid it can be about 10 vol% of the concentrated percolate volume.

Humic substance precipitation commences at pH 4.5-4.0 with possible formation of foam wh ich can be reduced and control led by add ing smal l quantities of anti-foaming agent, for example of silicone type; the acidification and precipitation system is provided with agitation means, means for bleeding and treatment of vapou rs and uncondensables such as carbon d ioxide, hydrogen sulphide and weak inorgan ic and organic acid substances volatile under said pH and temperature cond itions; consequently th is stage also contributes to purification of humic substances from substances which would reduce their quality, for example dangerous sulphides of unpleasant odour.

The humic substances are then subjected to a solid/liquid separation stage achieved by one or more known methods such as filtration, including vacuum filtration, centrifugation, decantation, floatation, etc. To improve the efficiency of these operations, it can be opportune to add small quantities, g en era l ly l ess tha n 1 .0 vol % , of polymer floccu l ation ag ents su ch as polyacrylates, polyacrylamide based cationic polyelectrolytes, additives which in any event do not influence final product quality. On termination of these stages the following are obtained:

- an acid solution of inorganic salts at pH 1 -3, preferably 2.0, in a quantity of 20-90 vol % of the su spen s ion previou sly obta i ned by acid ifi cation , contain ing a part of the fulvic acids (yel low coloration) and other water soluble non volatile organic substances present in the starting percolate; this solution is fed to a neutalization section at pH greater than 4 and then to disposal or to a concentration and crystallization stage for separation by precipitation in particular of the al kal ine and heavy metal salts, ma in ly chlorides and sulphates, while the condensate waters are recovered and recycled to the next wash section or fed to discharge after possible treatment.

- a concentrated acid suspension of crude humic substances of p H 1 -3, preferably 2.0, in a quantity of 80-1 0 vol% of the crude humic substance suspens ion previously obta ined by acid ification of the concentrated percol ate , with d ry res id u e at 1 05°C of 1 0-80 wt% of crude humic substances, consisting mostly of humic acid and to a lesser extent of fulvic acid. The crude humic substances are then dissolved as soluble alkaline humates by adding an aqueous solution of al kal ine hydroxide, preferably potassium, to pH 5.0-10.0, preferably pH 7.0; an aqueous solution of crude humic substances results which, possibly diluted, can be used as a soil improver in agriculture after qualitatively and quantitatively verifying compliance with the analytical limits provided by current regulations for products of similar origin such as sludge from mun icipal effluent water purifiers and composts from the S.U.R. organic fraction.

If considered necessary, before being d issolved with the aqueous solution of alkaline hydroxide, the crude humic substances are purified by washes with water, possibly deriving from purification of the condensates produced in the evaporation stages of the present process (Fig. 1 ), acidified to pH <7 with inorganic acid, for example sulphuric acid and/or hydrochloric acid and/or phosphoric acid , al l by known methods with cycl ic or continuous washes.

A suspen sion of pu rified h u m ic su bstances is obta ined with d ry residue at 105°C of 10-80 wt%, preferably 40%, at pH 5-7, and with low salinity expressed as dry residue at 600°C of less than 1 5 wt%, preferably 5 wt%.

If considered necessary, the aqueous solution of crude or purified humic substances solubilized as al kaline humates can be further purified by known treatment with sol id adsorbent prod ucts such as active carbons, kaol i n s , cl ay etc . to re move a n y org a n i c m icrocontaminants such as alkylphthalates, in particular 2-ethyl-hexylphthalate, nonyl- and octyl-phenols, bisphenol A.

The aqueous solution of crude or purified humic substances described above, besides being used after possible dilution as a soil improver for crops in agriculture in compliance with qualitative and quantitative limits provided by regulations, can be variously transformed into the following forms similar to those existing on the humic substance market:

- powder or granulate product, moisture content 1 0-30 wt%, obtained by drying for example in lagoon pools and exposure to air, electrically heated or microwave ovens, infrared rays, etc.,

- product as iron (II) humate solution obtained by adding ferrous sulphate to the basic solution, - suspended or dried product of calcium or magnesium humate obtained by adding CaO, Ca(OH) ₂ , or MgO or Mg(OH) ₂ , to pH >7, with precipitation of insoluble calcium or magnesium humates at basic pH.

The following examples illustrate the present invention but without limiting its scope.

Example 1 )

Successive incremental quantities (ml) of an aqueous 37.45 wt% sulphuric acid solution, density 1 .28 g/ml were added at ambient temperature under continuous agitation, to 100 ml of filtered percolate as such (sample 1 p) originating from a "mature" S.U.R. dump (A) with less than 500 mg/l of suspended solids, of dark brown colour, having the characteristics stated in Table 1 , while measuring the pH with a pH meter provided with a calibrated glass electrode, and recording the values at constant pH for each acid addition.

Effervescence is initially observed with foam production which is reduced and controlled by adding silicone antifoaming agent (0.2 ml of 10% Dinapan 16WD solution). At about pH 4 a flocky brown precipitate begins to form , with the solution colour clearing towards yellow, effervescence and foaming cease, and sulphuric acid addition is continued .

At pH 2 sulphuric acid add ition is interru pted and a portion of the suspension was placed in a test tube and centrifuged at 3200 rpm for 10 minutes and the supernatant separated as clear solution. Sulphuric acid was added to this; no further precipitate formation was observed, thus precipitation was considered virtually complete. The entire product obtained is centrifuged in a suitable laboratory apparatus at 3200 rpm for 1 0 minutes and the clear supernatant separated from the precipitate, the bottom suspension consisting of moist crude humic substances of 10 g (sample HS1) with the chemical characteristics given in Tab.2.

Tab.3. shows for the said sample (1p) the quantities, expressed in volume and weight, of 37.45 wt sulphuric acid added and the pH values obtained after each addition; at pH 2.21.97 g of pure sulphuric acid (20.1 mgmoles) were used per 100 ml of percolate as such.

2000 ml of the said percolate (sample 1p) were concentrated by evaporation in a Rotavapor laboratory apparatus at a temperature of 70°C under vacuum at a pressure of 46 KPa for about three hours until a volume reduction of 11 times is reached, to obtain 182 ml of concentrated percolate (sample 1 pc, characteristics in Tab.1 ) of dark brown colour and 1818 ml of aqueous condensate. After cooling to ambient temperature, quantities of sulphuric acid are added to 100 ml of concentrated percolate, sample 1pc (corresponding to 1100 ml of percolate as such), and the pH is measured until complete humic substance precipitation, in the same manner and with the same observations as for the previously described sample 1p; after centrifugation 41.8 g of moist crude humic substances (sample HS1c) were obtained with the characteristics given in Tab.2.

Tab.3 shows the volumes (ml) and weight (g) of sulphuric acid used against pH for:

1 ) Sample 1 p per 100 ml of percolate as such;

2) Sample 1 pc per 100 ml of percolate concentrated 11 times (corresponding to 1100 ml of percolate as such);

3) Sample 1pc normalized to 100 ml of percolate as such (corresponding to 9.09 ml of concentrated percolate). The comparison shows that 5.71 g (5.82 mgmoles) of sulphuric acid were used per 100 ml of concentrated percolate (1pc) which by calculation correspond to 0.519 g (5.29 mgmoles) of sulphuric acid per 100 ml of percolate as such prior to concentration; while for the non-concentrated sample (sample 1p) a much higher quantity, 1.97 g (20.1 mgmoles), of sulphuric acid per 100 ml of percolate as such (sample 1p) were required, with an increase of about 3.7 times on this consumption.

Tab.2 shows the differences between the chemical characteristics of the two samples, in particular the concentrated product (sample HS1c) shows a higher dry residue at 105°C, 23.50%, a good humic and fulvic carbon level, low levels of heavy metals, and a high level of soluble alkaline salts (sodium, potassium) possibly reducible by subsequent washes.

This example highlights the novelty of the invention which consists in implementing the innovative acid precipitation on the concentrated percolate obtained by thermal evaporation, hence achieving an important reduction in the required acid quantity with consequent economic advantage.

With regard to the possible contamination of the percolate as such (sample 1 p) and of the relative concentrate (sample 1 pc) by dangerous organic compounds, the following were also sought in these samples by normal analytical methods of adequate sensitivity and specificity:

- polychlorobiphenyls (PCB);

- aromatic polycyclic hydrocarbons (APH) (naphthalene, benzo(e)pyrene, acenaphthylene, acenaphthene, fluorine, phenanthrene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(123cd)pyrene, dibenzo(ah)anthracene, benzo(ghi)perylene, dibenzo(al)pyrene, dibenzo(ae)pyrene, dibenzo(ai)pyrene, dibenzo(ae)pyrene);

- carcinogenic halogenated aliphatic compounds (bromoformio, 1,2- dibromomethane, chlorodibromomethane, bromodichloromethane);

- non-carcinogenic chlorinated aliphatic compounds (1 ,1 -dichloroethane, 1,2- dichloroethane, 1 ,1 ,1-trichloroethane, 1 ,2-dichloropropane, 1,1,2- trichloroethane, 1 ,2,2-trichloropropane, 1 ,1 ,2,2-tetrachloroethane)

- carcinogenic chlorinated aliphatic compounds (chloromethane, dichloromethane, chloroform, vinyl chloride, 1 ,2-dichloroethane, 1,1- dichloroethylene, trichloroethylene, tetrachloroethylene);

- chlorinated aromatic compounds (chlorobenzene, 1 ,2-dichlorobenzene, 1,4- dichlorobenzene, 1 ,2,4-trichlorobenzene);

- aromatic organic solvents (benzene, toluene, ethyl benzene, styrene, xylenes, isopropylbenzene).

The relative results for all the aforesaid organic compounds were of a content less than the limits of measurability of the analytic methods of 1 mg/kg. The following were also less than the respective analytical measurement limits:

- total hydrocarbons (< 10 mg/kg);

- C<12 hydrocarbons (< 5 mg/kg);

- C>12 hydrocarbons (< 5 mg/kg).

Consequently even after concentration by 11 times the "mature" dump percolate (A) did not show contamination by said dangerous organic compounds with the specified analytical measurement limits.

Example 2) 2000 ml of "mature" dump percolate (A) as in Example 1) were concentrated in the laboratory with the same method, temperature and pressure as in Example 1) to obtain 166 ml of 12 times concentrated percolate (sample 2pc).

Successive quantities of 75 wt% phosphoric acid (d:1.5) were added under agitation at ambient temperature to a 100 ml portion of said concentrated percolate while measuring the pH continuously, as in the previous example; the quantities by volume and weight (ml and g) against pH are shown in Tab.4 per 100 ml of concentrated percolate and for the quantity of 8 ml of concentrate corresponding to 100 ml of non-concentrated percolate as such.

It can be seen that the humic substance precipitation commences, as in Example 1), at pH 4.4 and finishes at pH 2.3; the phosphoric acid used is 143 mgmoles per 100 ml of concentrated percolate and 11.48 mgmoles per 100 ml of percolate as such.

To improve the filterability of the precipitate, a solution of flocculant, Hydrapol C180 (80 mg/100ml), was added thereto, then after agitation the mixture was filtered through filter paper (black band) under vacuum (0.8 KPa of residual pressure); moist humic substances were obtained for 31.7% w/w of the concentrated percolate, with dry residue of 26 wt% at 105° (R105).

The use of phosphoric acid enables humic substances containing phosphates to be obtained, usually used as fertilisers in agriculture, hence enabling the raw materials used in the present invention to be upvalued.

Example 3) An industrial concentrated percolate was used obtained by thermal evaporation under vacuum at a plant operating in a "mature" dump (B) having the following characteristics:

pH: 9.6

dry residue 105°C (R105): 14.1 wt%

dry residue 600°C (R600): 10.0 wt%

organic substances (R105- R600): 4.37 wt%

chlorides (CI): 3.9 wt%

sulphates (SO4): 0.4 wt%

200 ml of said percolate (sample 3pc) were heated to 65°C, to simulate possible precipitation by acidification at the concentrator exit temperature, then while maintaining the sample heated, progressive quantities of 37.45 wt% sulphuric acid were added in the same manner as in Example 1), while continuously measuring pH, which at the end of precipitation was pH: 2.2; 22 ml of sulphuric acid were required (equal to 11 vol% of the concentrated percolate).

Tab 5 shows the quantities, expressed in volume and weight, of 37.45 wt% sulphuric acid added to 100 ml of concentrated percolate (sample 3pc) and the pH values obtained after each addition; 53.8 mgmoles/1 OOml of concentrated percolate were required in total, a value very similar to that found in Example 1) of 58.2 mgmoles/1 OOml of a different concentrated percolate.

Crude moist humic substances (7.1 wt% of sample 3pc) were separated from the obtained suspension by centrifugation, as in Example 1), with dry residue 105°C: 28.9 wt%; dry residue 600°C: 17.1 wt%; (R105- R600): 10.8 wt%. The supernatant, a clear yellow-brown solution, is 92.9 wt% with R105: 14.67 wt% and R600: 12.5 wt%; (R105- R600): 2.17 wt%.

To verify the efficiency of purification from the soluble salts by water wash, an equal quantity (ratio 1/1 by weight) of water acidified to pH 1 with sulphuric acid was added; after normal mixing by agitation, centrifugation was used to separate the supernatant consisting of a clear yellow solution, from the washed humic substance precipitate; R105; R600; chlorides; sulphates were determined on both fractions; four washes were carried out in successive sequence.

Tab. 6 shows the analytical results, from which it can be observed that:

- in the supernatant the quantities extracted reduce by about 50 wt% for each wash on a 1/1 wt ratio wash basis; after the 4th wash, the values of the determinations made are reduced to about 10% of the initial value, indicating a satisfactory capacity for extracting the soluble salts;

- in the precipitated humic substances it can be seen that at the 4th wash R105 is reduced by 10.7 wt%; R600 is reduced by 10.4 wt%, while the organic substances (R105-R600) are 11.5 wt%, virtually unvaried. These results demonstrate the facility for purifying the humic substances from soluble salts by washes with water, better if acidified. In an integrated technology system, water originating from the condensates of the thermal concentration stage can be used, including that under vacuum, as indicated in the process diagram of Fig.1.

Example 4)

20 ml of the silicone antifoaming solution used in Example 1) were added under agitation to 25 kg of industrial concentrated percolate (sample 4pc) originating from the plant operating at the same dump (B) as Example 3) but of a different period, with the following characteristics:

pH: 9.6

density 1 .1 g/ml

dry residue 105°C (R105): 13.8 wt%

dry residue 600°C (R600): 10.5 wt%

organic substances (R105- R600): 3.3 wt%

calcium (Ca): 0.22 wt%

sodium (Na): 3.0 wt%

magnesium (Mg): 0.1 wt%

and, while slowly checking the effervescence and the relative foams, 2.7 l itres of 37.45 wt% sulphuric acid were added at 20°C to pH 2.1 ; a dark brown flocky precipitate as obtained to which 25 g of Idrapol C1 80 flocculant are added ; the product is maintained u nder ag itation for 1 hour and then filtered by gravity through non-woven polypropylene cloth , type Polyfelt TS20(4.01 ), separating the precipitate and obtaining 2.5 kg of crude moist humic substances.

A 10 g fraction of crude moist hum ic substances is withdrawn and washed with water acidified to pH 1 with sulphuric acid in a 1 /1 v/v ration of crude humic substances/water followed by centrifugation and separation of the precipitate; a total of four washes were carried out in successive steps for pu rification from the water-soluble salts. A sam ple of pu rified h u m ic substances is obtained (sample HS4). The results of the analysis of sample HS4 expressed in wt% on the dry residue at 105°C, and the methods used are given in Tab. 7. In particular the high dry residue at 600°C can be observed together with high calcium (Ca) content (9.5 wt%) and high sulphate (SO4) content (30.5 wt%), in a molar ratio (0.7:1 ) such as to assume the presence of most of the sulphate ion (SO4) as calcium sulphate (CaSO4).

The composition of sample HS4, partially reproduced below, highlights a reduced chloride (CI), sodium (Na) and potassium (K) content:

sulphates (SO4): 30.5 %s/s

chlorides (CI): 0.37 %s/s

calcium (Ca): 9.5 %s/s

silica (SiO2): 5.9 %s/s

sodium (Na): 0.22 %s/s

potassium )K): 0.08 %s/s

It can hence be sent that by acidification with sulphuric acid, together with th e h u m ic su bsta nces there al so preci pitate a l ka l i ne earth metal sulphates, in particular calcium sulphate, and colloidal silica. These compounds are insoluble in water acidified to pH 1 with sulphuric acid used for the washes, whereas the alkaline metal salts, in particular chlorides (CI) of sod ium (Na) and potassium (K) are present in a total concentration of less than 1 %.

It can be seen that calcium sulphate (CaSO4) and colloidal silica (SiO2) are also used as soil improvers and soil pH correctors in agriculture (calcium sulphate); consequently from calcium-rich percolates, by using the same tech nology, prod uct m ixtu res can be obta ined wh ich can perform several useful functions in agriculture.

A small portion of the sample HS4 was dried in an oven in air at 105°C to constant weight, for two hours; about 0.6 g were used mixed with about 200 mg of potassium bromide (KBr) and a tablet produced by compression; on this latter an FT-IR spectrum was obtained compared with the spectra of KBr tablets produced by the same method from a commercial humic substance sample extracted from leonardite (COM2) and of standard calcium sulphate. The spectra comparison shows the simultaneous presence of absorption bands characteristic of commercial humic substances (COM2) and of calcium sulphate, confirming the presence of this latter in Samp/HS4.

With regard to possible contamination by dangerous non-volatile organic compounds, it can be seen in Tab.7 that even in the dump percolate (B) and in the purified humic substances, most of those sought are not present at concentrations greater than the limiting quantities of analytical methods, those found being present at concentrations less than the regulation limits current in Italy and the European Union relative to use of purification sludges as agricultural soil improvers, with particular reference to micro- contaminants such as polychlorodibenzodioxins/furans (PCDD/PCDF), 2- ethyl-hexylph thai ate, aromatic polycyclic hydrocarbons (APH), polychlorobiphenyls (PCB).

Finally with regard to biological contamination in the dump percolate (B), in concentrated percolate obtained therefrom by evaporation and in purified humic substances HS4, the total coliform concentrations found pass from 18000 UFC/100ml in the percolate to <1 UFC/100ml both in the concentrated percolate and in purified humic substances HS4. This demonstrates how the percolate concentration process by thermal evaporation under vacuum conducted at high temperature is effective in sterilizing the concentrated percolate. A further guarantee of precipitated humic substance sterilization is the acid treatment of the concentrated percolate to pH 2. Salmonella was instead not found, either in the dump percolate (B) or in the concentrated percolate or in the purified humic substance sample HS4.

Example 5)

1ml of antifoaming agent (0 wt% Dinapan 16WD) and progressive quantities of 37.45 wt% hydrochloric acid (density: 1.186 g/ml) are added under agitation to 200 ml of industrial concentrated percolate originating from the same dump (B) as Example 3-4) but of a different period, with the following characteristics:

pH: 10

dry residue 105°C (R105): 15.4 wt%

dry residue 600°C (R600): 11.1 wt%

organic substances (R105- R600): 4.3 wt%

chlorides (CI): 3.2 wt%

sulphates (SO4): 0.6 wt%

Tab.8 shows the hydrochloric acid volumes and weights (ml and g) against pH.

Precipitation commences at pH: 4.3, as in the previous examples, of a dark brown flocky solid, and is completed at pH: 2.0. A total of 15.6 ml of 37.45 wt% hydrochloric acid (density: 1.186 g/ml), 6.85 g of pure acid, corresponding to 3.42 g of acid per 100 ml of concentrated percolate (sample 5pc) equivalent to 95 mgmoles of acid (HCI).

After adding the flocculant followed by centrifugation, as in the previous examples, a crude moist humic substance solid was separated (sample HS5g) of 20.0 g, equal to 10% of (5pc) with dry residue at 105°C of 25wt%. After drying at 105°C to constant weight, a portion of HS5g was subjected to four successive washes with water acidified to pH approximately 1 with hydrochloric acid in the manner described in Example 4. A purified moist humic substance solid was recovered (sample HS5) with dry residue at 105°C of 36 wt%. When dried at 105°C the sample HS5 has a weight equal to 26% of the weight of HS5g dried at 105°C from which it was obtained.

Tab.9 shows the characteristics of the samples HS5g and HS5.

From Tab.9 it can be seen that by using hydrochloric acid for humic substance precipitation, the presence of calcium sulphate and other possible inorganic compounds insoluble in the purified humic substances is drastically reduced. In this respect, the sample HS5 presents a dry residue at 600°C of 3.7% (equal to 10% of the dry residue at 105°C) while the sample HS4, rich in calcium sulphate, presents a dry residue at 600°C of 17.3% (equal to 48% of the dry residue at 105°C).

Moreover, as shown in Examples 1), 2), 3) it is also demonstrated in this example that precipitation commences at pH less than 5 and is completed at pH less than 2.5 for different percolate types and different inorganic acids.

Small portions of samples HS5g and HS5, oven dried in air at 105°C to constant weight for two hours, were mixed with potassium bromide and formed into tablets, on which FT-IR spectra were obtained in the same manner as for HS4 in Example 4. The HS5g and HS5 spectra are very similar to each other, indicating the absence of significant variations following the wash process. Both are well superimposable on that of the commercial product.

The spectra of samples HS5g and HS5 also show good superimposability with the spectrum of said reference material. Example 6)

20.0 kg of percolate as such of a mature Italian dump (C) (sample 6p) was concentrated 18 times in the laboratory, to obtain 1 .10 kg of concentrated percolate (sample 6pc) by the method stated in the previous examples and with the characteristics given in Tab. 1 0 in which for the concentrate (6pc) a net reduction of ammoniacal nitrogen and sulphides is particularly noted.

37.45 wt% sulphuric acid was added to the concentrated percolate (6pc) to pH 2.0 in the same manner as in Example 4) to obtain a dark brown flocky precipitate which when separated from the supernatant (clear solution of mother liquors) by centrifugation forms the crude moist humic substance sample not purified by water washes; potassium hydroxide (KOH) was added to th is hu m ic substance suspension sample until neutral ity (pH 7.0) was reached to obtain an aqueous solution of soluble potassium humates (sample HS6) . The characteristics of sa id sam ple com pared with a com mercial product (COM 1 ) of potassium humate solution and of a further commercial humic substance powder product (COM2) extracted from leonardite are shown in Tab. 1 1 .

It can be seen in particular that the sample (HS6) in solution contains a humic carbon quantity similar to the commercial sample in solution (COM1 ), the soluble inorganic salt quantities (residue at 600°C) are similar and consist of alkaline salts (potassium, sodium) of chlorides, sulphates, in particular the powder sample (COM2) shows high phosphate quantities, the heavy metals are low and virtual ly si m i lar between the th ree sam ples and with in the regulation limits for agricultural applications; the two commercial samples obtained by extraction from leonard ite show h igh quantities of iron , wh ich however is used as a soil improver in agriculture. Consequently it has been demonstrated that products of composition similar to that of the various different commercial products used in agriculture can be prepared from humic substances obtained by acid precipitation from concentrated percolate.

Example 7)

The samples of the previous Example 6) (HS6) and (COM1) in the form of humic substance solutions were analyzed by th Chemical-Agrarian Analysis Laboratory of the Agrarian Biotechnology Department of the University of Padua (Italy) to determine their biostimulant activity in accordance with the methods indicated in:

- Fertilias Agrorum 1(1): 47-53 -Serenella Nardi, Andrea Ertani, Giuseppe Concheri, Diego Pizzeghiello - "Metodi di determinazione dell'attivita biostimolante" (Methods for determining biostimulant activity)

Tab.12 shows the humic substance characteristics, namely: density, total organic carbon (TOC), total extractable carbon (TEC), humic acids (HA), fulvic acids (HF); humification degree HD=(HA+HF)/TEC; humification rate HR=(HA+HF)/TOC; humification index HI=[TEC-(HA+HF)]/ (HA+HF).

The two samples show similar values, both with satisfactory humification (HD, HR, HI), typical of "mature" products.

The molecular weight distribution, Tab. 13, determined by gel permeation (LPLC), is similar for the two samples, with Sample HS6 showing a greater quantity of 1st and 3rd fraction, generally correlated with the degree of humic substance maturation and biological activity. The biostimulant activity determined by the biotest "AUDUS", Tab.14, in which the two samples were treated with increasing quantities of 3-indoleacetic acid and gibberellic acid (GA3) to determine the inhibition of radical development on watercress and stimulation of hypocotyl elongation on wh ite Trieste chicory, obtained maximum auxinic activity for Sample HS6, while neither sample showed any gibberellinic activity.

Finally Tab. 1 5 shows evaluations of biostimulant activity on 14 day maize seedlings;

the test, which consists of a hydroponic cultivation of maize seedlings for 1 2 days with da ily replacement of the nutrient solution , fol lowed by a period of 48 hours in wh ich the seedlings are brought into contact with two concentrations (1 .0 ml and 0.5 ml per litre) of the two humic extract samples, showed that Sample HS6 gives a better and good growth of the seedling fresh weight.

Consequently the example shows that even crude humic substances, as obtained by the process of the present invention, even without washing to reduce soluble salts (purification), show good characteristics for application as soil improvers in agriculture.

TAB.1 - Percolate characteristics (Bellolampo, Sicily) as such (sample 1p) and concentrate sample 1pc) - Example 1 - TAB. 1 - (continued)

Samples u.m. 1 p 1 pc

Pyrene mg/kg <1 <1

Benzo(a)anthracene mg/kg <1 <1

Chrysene mg/kg <1 <1

Benzo(b)fluoranthene mg/kg <1 <1

Benzo(k)fluorantene mg/kg <1 <1

Benzo(a)pyrene mg/kg <1 <1 lndeno( 123cd)pyrene mg/kg <1 <1

Dibenzo(ah)anthracene mg/kg <1 <1

Benzo(ghi)perylene mg/kg <1 <1

Dibenzo(al)pyrene mg/kg <1 <1

Dibenzo(ae)pyrene mg/kg <1 <1

Dibenzo(a,i)pyrene mg/kg <1 <1

Dibenzo(ah)pyrene mg/kg <1 <1

Total Hydrocarbons mg/kg < 10 <10

C< 12 Hydrocarbons mg/kg <5 <5

C> 12 Hydrocarbons mg/kg <5 <5

CARCINOGEN IC HALOGENATED ALIPHATICS

Bromoform mg/kg <1 <1

1 ,2-Dibromoethane mg/kg <1 <1

Clorodibromometano mg/kg <1 <1

Bromodichlorometane mg/kg <1 <1

NON-CARCINOGENIC CHLORI NATED

ALIPHATICS

1 , 1 -Dichloroethane mg/kg <1 <1

1 ,2-Dichloroethylene mg/kg <1 <1

1 , 1 , 1 -Trichloroethane mg/kg <1 <1

1 ,2-Dichloropropane mg/kg <1 <1

1 , 1 ,2-Trichloroethane mg/kg <1 <1

1 ,2,3-Trichloropropane mg/kg <1 <1

1 , 1 ,2,2-Tetrachloroetane mg/kg <1 <1

CARCINOGEN IC CHLORINATED ALIPHATICS

Chlorometane mg/kg <1 <1

Dichlorometane mg/kg <1 <1

Chloroform mg/kg <1 <1

Vinyl Chloride mg/kg <1 <1

1 ,2-Dichloroetane mg/kg <1 <1

1 , 1 -Dichloroethylene mg/kg <1 <1

Trichloroethylene mg/kg <1 <1

Tetrachloroethylene mg/kg <1 <1

CHLOROBENZENE

Chlorobenzene mg/kg <1 <1

1 ,2-Dichlorobenzene mg/kg <1 <1

1 ,4-Dichlorobenzene mg/kg <1 <1

1 ,2,4-Trichlorobenzene mg/kg <1 <1

AROMATIC ORGANIC SOLVENTS -

Benzene mg/kg <1 <1

Toluene mg/kg <1 <1

Ethylbenzene mg/kg <1 <1

Styrene mg/kg <1 <1

Xylene (mixed isomers) mg/kg <1 <1

Isopropylbenzene (Cumene) mg/kg <1 <1 TAB.2 - Characteristics of Humic Substances from percolate (A) as such (sample HS1) e concentrate (sample HS1c) -

Example 1-

TAB. 3 - Humic Substance precipitation from percolate (A) - 37.45 wt% sulphuric acid quantity (d: 1 .28 Kg/dm ³ ) referred to 100mL of percolate as such. - mL H ₂ SO ₄ vs pH)

- sample 1 p: percolate as such (100 mL)

- sample 1 pc: percolate concentrated 1 1 times (100 mL)

- Example 1 -

TAB. 4 - Humid Substance precipitation from percolate concentrated (A) - 75 wt% phosphoric acid quantity (d: 1 .57 Kg/dm ³ ) referred to 100mL of percolate as such - (ml_ H ₃ PO ₄ vs pH)

- sample 2pc: percolate concentrated 12.1 times, 100mL

- Example 2 -

TAB. 5 - Humid Substances precipitation from industrial concentrated percolate (B) - 37.45 wt% sulphuric acid quantity (d: 1 .28 Kg/dm ³ ) referred to 100mL of concentrated percolate - (ml_ H ₂ SO ₄ vs pH) - sample 3pc.

- Example 3 -

_{ttdt pr} ec _ipi ae mo _i s

l _ittt su _p enaan souon

S H _ibt umcusances

TAB.6 - Humid Substances purification (sample HS3) - by washed with water acidified to pH 1 with sulphuric acid -

- Example 3 -

R 105°C R 600°C R 105°C-R600°C Chlorides Sulphates

Wash No.

(%) (%) (%) (mg/L) (mg/L)

0 14,67 12,50 2,17 36200 52700

1° 7,60 5,20 2,40 13000 22000

2° 3,98 2,90 1,00 6900 14000

3° 2,33 1,70 0,63 3100 7800

4° 1,48 0,84 0,21 2600 5000

0 28,9 17,1 11,8

1° 23,2 13,2 10,0

4° 18,2 6,7 11,5

- Chemical characteristics purified Humic Substances dry matter from concentrated percolate (B) (Samp.HS4) and of percolate (B) as such - Example 4 - TAB. 7 - (continued)

Sample Sample m.u.. HS4 m.u. percolate (B)

IPA

Naphthalene mg/Kg dry matter <1 mg/Kg <5

Benzo(j)fluoranthene mg/Kg dry matter <1 mg/Kg nd

Benzo(e)pyrene mg/Kg dry matter <1 mg/Kg nd

Acenaphthylene mg/Kg dry matter <1 mg/Kg <0,5

Acenaphthene mg/Kg dry matter <1 mg/Kg <0,5

Fluorene mg/Kg dry matter <1 mg/Kg <0,5

Phenanthrene mg/Kg dry matter <1 mg/Kg <0,5

Anthracene mg/Kg dry matter <1 mg/Kg <5

Fluoranthene mg/Kg dry matter <1 mg/Kg <0,5

Pyrene mg/Kg dry matter <1 mg/Kg <0,5

Benzo(a)anthracene mg/Kg dry matter <1 mg/Kg <0,5

Chrysene mg/Kg dry matter <1 mg/Kg <0,5

Benzo(b)fluoranthene mg/Kg dry matter <1 mg/Kg <0,5

Benzo(k)fluoranthene mg/Kg dry matter <1 mg/Kg <0,5

Benzo(a)pyrene mg/Kg dry matter <1 mg/Kg <0,5 lndeno(123cd)pyrene mg/Kg dry matter <1 mg/Kg <0,5

Dibenzo(ah)anthracene mg/Kg dry matter <1 mg/Kg <0,5

Benzo(ghi)perylene mg/Kg dry matter <1 mg/Kg <0,5

Dibenzo(al)pyrene mg/Kg dry matter <1 mg/Kg <5

Dibenzo(ae)pyrene mg/Kg dry matter <1 mg/Kg <0,5

Dibenzo(a,i)pyrene mg/Kg dry matter <1 mg/Kg <0,5

Dibenzo(ah)pyrene mg/Kg dry matter <1 mg/Kg <0,5

Total Hydrocarbons mg/Kg dry matter <10 mg/Kg nd

2-ethysil phthalate mg/Kg dry matter 32,6 mg/Kg nd other phthalates mg/Kg dry matter <5 mg/Kg nd

ng l-TE/Kg dry

2,3,7,8-PCDD/F matter 15,0 ng l-TE/Kg 0,017

Biocides and phytopharmaceutical

substances (99 compounds sought) Mg/Kg ND Mg/Kg <0,01 - <50

Total Coliforms UFC/100g absent UFC/100mL 18000

Salmonellas - absent - absent

TAB. 7/1 - Organic and inorganic contaminants present in purified humic substances from concentrated percolate (B) (Samp.HS4) e maini regulatory references - Example 4 -

(1 ) acenaphthene, phenanthrene, fluorene, fluoranthene, pyrene, Benzo(a)pyrene, Benzo(b)fluoranthene, Benzo(j)fluoranthene, Benzo(k)fluoranthene, Benzo(ghi)perylene, lndeno(1 ,2,3-cd)pyrene

(2) PCB markers: # 28, #52, #101 , #1 18, #138, #153, #180

(3) Sum of at least: Lindane, endosulfan, trichloroethylene, tetrachloroethylene, chlorobenzene

TAB. 8 - Precipitation HS from concentrated industrial percolate (B) - amount hydrochloric acid to 37.45% w / w (d: 1 ,186 Kg/dm3) referred to 100mL of concentrated percolate - (mL HCI vs pH)

- 5pc sample - example 5 -

TAB. 9 - Physical and Chemical characteristics of HS precipitated with HCI percolate (B) concentrated before and after purification with acid wash - sample HS5g and HS5

- Example 5 -

Sample

u.m. HS5 g HS5

Residue a 105°C % mass 25 36

Residue a 600°C % mass 14,6 3,7

Residue a 105°C - Residue a 600°C % mass 10,4 32,3

Total Phosphorus (P) mg/kg dry matter 842 597

TOTAL METALS -

Total Arsenic (As) mg/kg dry matter 12,7 17,4

Barium (Ba) mg/kg dry matter 9,02 3,44

Cadmium (Cd) mg/kg dry matter <1 <1

Total Chromium (Cr) mg/kg dry matter 193 550

Hexavalent Cromium (Cr) mg/kg dry matter <0,5 <0,5

Total Copper (Cu) mg/kg dry matter 15,2 37,2

Iron (Fe) mg/kg dry matter 1264 1250

Potassium (K) % dry matter 6,48 0,18

Manganese (Mn) mg/kg dry matter 21,9 <1

Molibdeno (Mo) mg/kg dry matter 6,46 16,6

Sodium (Na) % dry matter 12,7 0,25

Nickel (Ni) mg/kg dry matter 84,5 187

Lead (Pb) mg/kg dry matter <3 <3

Total Antimony (Sb) mg/kg dry matter <2 <2

Zinc (Zn) mg/kg dry matter 44 20,8

Aluminium (Al) mg/Kg dry matter 4835 2357

Boron (B) mg/Kg dry matter 512 537

Cobalt (Co) mg/Kg dry matter 20,4 50,3

Mercury (Hg) mg/Kg dry matter <1 <1

Tin (Sn) mg/Kg dry matter 75,6 233

Strontium (Sr) mg/Kg dry matter 7,73 <1

Magnesium (Mg) % dry matter 0,26 0,019

Calcium(Ca) % dry matter 0,31 0,059

Silicon (as Si02) % dry matter 2,0 8,0

ANIONS

Sulphates (S04) % dry matter 2,6 2,7

TAB. 10 - Chemical characteristics of percolate (C) as such (sample 6p) and concentrated

(sample 6pc).

- Example 6 -

- Chemical characteristics of (HS6) compared with commercial products (COM1 ) e (COM2).

- Example 6 - TAB. 12 - Agrinomic characterists of (HS6) compared with commercial products (COM1 ).

- Esempio 7 -

HD= HUMIFICATION DEGREE = (HA+HFJ/TEC

This is a quasi-quantitative parameter: in soils and peats it assumes intermediate values (70-80) even if generally very high; in humified materials (leonardite and humic extracts) it has values close to 100; in only slightly mature materials (non-mature composts and organic fertilizers) it assumes values close to zero;

HR= HUMIFICATION RATE = (HA+HF)/TOC

This is a quantitative parameter: the same considerations are valid as for HD;

Hl= HUMIFICATION INDEX = NH/ (HA+HF) where NH = TEC-(HA+HF)

This is lower the greater the quantity di humic substances in the soil: in humified peats and mature fertilizers it assumes values <0,5; in leonardites and derived humic extracts iti has values close to 1 ; in non-humified materials (non-mature composts and sludges, organic fertilizers) it assumes values >1 .

- Analyses of apparent molecular weights of (HS6) compared with commercial product (COM 1 ).

- Example 7 -

Interpretation of results

The literature on the subject considers the percentage abundance of 1 st fraction (molecular weights >100KD) and of 3rd frazione (molecular weights >250KDa) directly correlated with the degree of maturation of the humic substances and with the biological activity which they can exert.

From this viewpoint the humic extract HS6 presents una better division of the three fractions than the humic extract COM1 in that it shows a greater presence of 1st and 3rd fraction and a smaller presence of 2nd fraction.

- Determination of biostimulant activity by "AUDUS" bioassay of (HS6) compared with commercial product (COM1 ).

- Example 7 -

Interpretation of results

The humic extract samples were compared, by bioassay, with increasing quantities of 3 indoleacetic acid and gibberellic acid (GA3) to determine, respectively, inhibition of radical development on watercress and stimulation of hypocotyl elongation on white Trieste chicory.

Maximum auxin activity was found in the sample known as HS6. The tested samples did not show gibberellinic activity.

TAB. 15 - Determination of biostimulant activity of (HS6) on maize plants compared with commercial product (COM1 ).

- Example 7 -

Interpretation of results

The test consists of a hydroponic cultivation of maize seedlings for 12 days with daily replacement of the nutrient solution, followed by a period of 48 hours in which the seedlings are brought into contact with two concentrations (1 .0 ml and 0.5 ml per litre) of the different humic extracts. The determination showed that the humic extract sample HS6 gives an increase in the whole seedling fresh weight (about +15%) for both tested concentrations, with the most significant increases (+19%) in the hypogeous portion. In contrast, the sample COM1 showed an averagely negative trend.