FIELD OF THE INVENTION

The present invention relates to treatment of sewage, in particular treatment onboard boats, ships and other such vessels, and also to compositions for use in the treatment of sewage.

BACKGROUND OF THE INVENTION

Sewage is generated whilst a vessel is in use, e.g. a boat on a waterway such as a river or canal, or a boat at sea, especially in the case of vessels carrying any number of passengers. Thus, on a typical vessel at sea for any length of time, sewage must be routinely treated and discharged so as to avoid excessive buildup in the ship. It is contrary to local and maritime laws to discharge raw sewage into the sea or other waterways and there are strict regulations governing how sewage is to be treated so as to be in a state acceptable for discharge.

It is known to treat sewage on-board a vessel by contacting it with a chlorine- containing solution, allowing the resultant mixture to stand for a period of time to achieve an acceptable reduction in the bacterial count of the sewage, prior to discharging the treated sewage, e.g. into the sea. A number of problems exist with the current method, however. The known chlorine-containing compositions are hazardous both to store and to use, requiring protective clothing and adequate ventilation. The compositions are typically provided in liquid form, which are bulky and heavy, thus awkward to transport onto the vessel. After treatment with the chlorine-containing compositions, the resultant treated sewage has a very high pH, which must be reduced in a further chemical treatment by adding sodium bisulphate, before the treated sewage can be disposed of. Thus, existing methods are multi-step and expensive.

GB 2319521 describes day-to-day sanitisation of swimming pool water using a low dose, typically about 5 grams per 45 litres of water, of a water-soluble peroxy compound. US 7179389 describes a sewage treatment system in which hydrogen peroxide, glycolic acid and water are combined in situ and contacted with sewage. WO 2004/058650 describes treatment of waste water by first separating it into treated waste water and sludge and thereafter contacting the sludge with a peroxy compound so that further water can be separated from the sludge. None of these deal with the identified problems of sewage treatment.

It is also known for sewage to be discharged into the sea from land-based sewage sources, whether routinely or in the case of overload of sewage treatment plants. This causes deterioration in beach resort water.

Hence, an object of the present invention is to solve or at least ameliorate the above-identified issues with treatment of sewage, especially on-board boats, ships and like vessels prior to discharge. An object of preferred embodiments of the invention is to provide for sewage treatment on-board with reduced hazard to the equipment and to the users and/or with a step that is simplified, preferably involving fewer steps. An object of a specific embodiment is to provide for sewage treatment which can be carried out in a continuous or semi-continuous way.

SUMMARY OF THE INVENTION

The present invention provides a method for treating sewage, comprising combining the sewage with a water-soluble peroxy compound to form a mixture and incubating the mixture prior to discharge. The incubated mixture may then be discharged, e.g. into the sea, a waterway, a watercourse or into a subsequent sewage treatment station.

The present invention also provides the water-soluble peroxy compounds for such use.

DETAILED DESCRIPTION OF THE INVENTION

Sewage can thus be treated in a one-step method, without the need for an extra neutralising step. Sewage can be treated using compounds that are relatively non-toxic to handle and store. Sewage can be treated on board a vessel prior to discharge into a watercourse such as a river or the sea. Sewage can also be treated on land.

The treatment method can comprise combining the sewage with the disinfecting peroxy compound in a container such as a sewage treatment tank. Typically, peroxy compound is added to sewage in the tank, and treated sewage discharged after treatment.

The treatment may comprise combining the sewage with the peroxy compound by introducing the peroxy compound into a sewage stream. In this way, peroxy compounds may be added to or combined with sewage flowing in a stream and be mixed into and incubated in the stream, for example whilst being transferred to or pumped into another zone or tank in a treatment system. In other embodiments, the treatment may comprise introducing the compound into sewage flowing out to sea from a land-based sewage source, either raw or partially treated sewage.

During incubation, the peroxy compound is suitably contacted with the sewage and preferably mixed intimately with the sewage so that through such contact with the compound bacterial and other microbial contamination can be killed. Incubating the mixture can comprises agitating the mixture, for example using an impeller or other mixing device. On board a smaller, less stable boat or ship, by way of example, the agitating may be achieved via movement of the vessel, causing movement of the mixture being treated in a tank.

In embodiments of the invention in which peroxy compound is added to sewage in a stream, mixing and incubation may occur in the stream, while being pumped and / or transferred into other location or tank.

In use of the invention, the disinfecting peroxy compound kills contaminating microorganisms in the sewage, to reduce the microbial count so that the resultant treated water is regarded as acceptable for discharge. When used at sea, the treated water is clean enough to go into sea water. When used on an inland waterway, the water is treated so as to be acceptable for discharge into a sewer or watercourse. Regulations govern cleanliness of water for particular types of discharge, for example allowing discharge into the sea once a ship is a minimum distance from the shore, generally 12 miles or more.

Preferably, the treatment method comprising incubating the mixture so as to achieve at least a 4 log reduction in viable coliform bacteria in the sewage, more preferably at least a 5 log reduction. In particular embodiments, the reduction in bacterial count is at least 6 log.

The treatment suitably reduces the bacterial count to 10,000 or fewer microbes per 100ml_ of liquid (usually water), more preferably 1 ,000 or fewer, still more preferably 100 or fewer. In embodiments of the invention, described in more detail below, treating sewage produced a drop in coliform count below detectable limits.

Bacterial reduction may be related to incubation or exposure time. Generally the incubation time is 5 minutes or more, 10 minutes or more, or 15 minutes or more. In tests, incubation of about 20 minutes has reduced the bacterial count to a level acceptable for discharge into the sea. In a specific embodiment of the invention, 25 minutes contact time with compounds of the invention resulted in a drop in coliform count below detectable limits. The time period may be reduced with increased agitation.

The water-soluble peroxy compound for use in the invention is suitably a water- soluble salt. It can be an alkali metal salt, optionally a sodium or potassium salt; it may be an ammonium salt.

In particular embodiments of the invention, the water-soluble peroxy salt is a peroxy monosulphate salt. Examples of suitable peroxy salts are peroxysulphate (S0 ₅ ^2" ), peroxycarbonate (C0 ₄ ^2" ) or peroxyborate (B0 ₄ ^2" ).

In a specific embodiment of the invention, used in examples described below, the peroxy compound is a triple salt of potassium hydrogen peroxysulphate, potassium hydrogen sulphate and potassium sulphate. In one operation of the invention, sufficient peroxy compound is used to treat the sewage prior to discharge in accordance with maritime regulations. Generally, all methods comprise combining the sewage with the water-soluble peroxy compound in an amount of at least 25g of the peroxy compound per 80 litres sewage (about 0.31 g/L or more), preferably at least 40g of the peroxy compound per 80 litres sewage (about 0.5g/L or more), more preferably at least 48g per 80 litres sewage (about 0.6g/L or more), in particular from 50-300g of the peroxy compound per 80 litres sewage (from about 0.63g/L to about 3.8g/L). In two example protocols described below in more detail, about 100g of the pentapotassium bis (peroxy monosulphate) bis (sulphate) triple salt is combined with every 80 litres of sewage (about 1 .2 g/L). In other examples described below, in test exposures of 25 minutes a dose of 0.4g/L reduced faecal coliform numbers and doses of 0.5g/L and above reduced bacterial counts across the spectrum tested.

The peroxy compound is water soluble, and in embodiments of the invention the method comprises combining the sewage with a solution of the peroxy compound. The solution can be prepared with sea water or preferably fresh water; on-board boats and ships there is generally a source of fresh water available, or there may be water available at port or other dock. Solutions are easy to handle and the compounds of the invention are relatively non-toxic to use. In ships, often with cramped poorly ventilated spaces, there is an advantage in treatment chemicals that do not generate noxious fumes as do the known chlorine-based treatments. In an example described below in more detail, about 150ml_ of a solution of the triple salt is combined with every 80 litres of sewage.

In particular embodiments of the invention, use of the peroxy compounds enables further increase in efficiency of sewage treatment through a continuous process. Thus a method of the invention comprises simultaneously:- combining the sewage with the peroxy compound to form a mixture, incubating a mixture of sewage with a water-soluble peroxy compound, and

discharging a previously incubated mixture of sewage and a water-soluble peroxy compound. Hence, all three steps may occur at the same time in different stages of the treatment process, sewage being continuously treated. The method may be carried out in sewage treatment apparatus comprising a first zone in which sewage can be combined with a water-soluble peroxy compound, a second zone in which a mixture of sewage and a water-soluble peroxy compound can be incubated and a pump in combination with a conduit through which an incubated mixture of sewage and a water-soluble peroxy compound can be pumped for discharge.

The invention further provides apparatus for carrying out the method of the invention. A particular apparatus for continuous treatment of sewage on a vessel in the sea, comprises:- a container for sewage, in which the sewage can be combined with a water-soluble peroxy compound,

an incubation container, in which sewage combined with water-soluble peroxy compound can be incubated, and

an exit port for discharge of treated sewage from the vessel,

wherein the combining container is in fluid communication with the incubation container which is in turn in fluid communication with the exit port further wherein a first batch of treated sewage can be discharged into the sea whilst a second batch of sewage can be incubated and at the same time a third batch of sewage can be combined with water-soluble peroxy compound in a continuous treatment process. Optionally, the apparatus further comprises a holding tank, in which treated sewage can be temporarily stored on board prior to discharge, suitable for when it is intended to start treatment at a location where treated sewage may not be discharged, such as in port or close to shore, and discharge treated sewage at a second location, e.g. more than 12 miles off shore.

The invention also provides compositions. Thus the invention provides a water- soluble peroxy compound, for use in treatment of sewage, preferably for use in treatment of sewage on board a vessel. The water-soluble peroxy compound is as defined elsewhere herein, thus compositions of the invention for the specified uses suitably comprise or consist of a water-soluble salt of the peroxy compound. The salt can be an alkali metal salt, optionally a sodium or potassium salt; it may be an ammonium salt. In particular embodiments of the invention, the water-soluble peroxy salt is a peroxy monosulphate salt. Examples of suitable peroxy salts are peroxysulphate (S0 ₅ ^2" ), peroxycarbonate (CO ₄ ^2" ) or peroxyborate (B0 ^2" ). In a specific embodiment of the invention, the peroxy compound is a triple salt of potassium hydrogen peroxysulphate, potassium hydrogen sulphate and potassium sulphate.

The compositions of the invention may be provided in combination with instructions for their use in sewage treatment, suitable instructions including recitation of weight of the compound per volume of sewage (as herein defined), to achieve desired reduction in bacterial count as described elsewhere herein using the compositions.

Still further provided by the invention is the use of the peroxy salts and compositions comprising or consisting of the salts for use in manufacture of a composition for sewage treatment.

Conveniently, the invention is provided in kit form, being the compound together with information enabling the user to use it at suitable strength to achieve sewage treatment. A kit of the invention for sewage treatment hence comprises:-

(i) a water-soluble peroxy compound of the invention; and

(ii) written instructions as to how to use the compound for sewage treatment.

The kit can be made up of a container having an amount of the compound therein plus an instruction sheet or manual. The container may be designed so that once filled with water a solution of the compound is obtained with suitable strength for treatment of a particular volume of waste water. As an example, 100g of compound in a container that holds slightly more than 1 litre is accompanied by instructions to add 1 Litre of water to make a solution to treat 100 litres of waste water. The written instructions may guide the user to use the compound for treatment of sewage according to any of the methods described herein. Thus they may indicate a dose of 25g/80L (about 0.31 g/L) or more, or 40g/80L (about 0.5g/L) or more. As a specific example, the kit may direct use at 1g/L (being in the range of 0.5g/L or more).

In a specific embodiment of the invention there is provided a method of treating sewage, comprising combining the sewage with pentapotassium bis (peroxy monosulphate) bis (sulphate) to form a mixture, and incubating the mixture prior to discharge. A specific kit for sewage treatment, comprises (i) pentapotassium bis (peroxy monosulphate) bis (sulphate); and (ii) written instructions to use the compound for sewage treatment according to any method of the invention.

The invention is now further described in specific embodiments with reference to the accompanying examples.

EXAMPLES

Example 1

In initial tests, a dose of pentapotassium bis (peroxy monosulphate) bis (sulphate) of 0.6g/L was found to be effective to treat marine sewage effluent.

Example 2

Compositions of the invention were further tested for their effectiveness at treating sewage.

Approx. 4 litres of sewage was obtained and eight samples of treatment solution doses of different strengths of pentapotassium bis (peroxy monosulphate) bis (sulphate) were created plus one control with no active agent. Nine bottles were each filled with 400ml of sewage and the doses transferred to pipettes located above each bottle, so they could be released simultaneously. Once all doses were ready we quickly released them into the nine bottles containing sewage and timed 25 minutes of contact. Separately, nine bottles containing 9 ml of Difco Neutralizer Ref 281910 were prepared. After the 25 minutes 1 ml from each of the bottles containing sewage plus treatment was removed and added to each bottle containing the 9 ml of Neutralizer. 4 minutes contact time was allowed.

The bacterial count of each bottle was then determined and the results were as shown in Table 1 :

Table 1

[NB the lower limit of detection was 100, thus <100 indicates the count was lower than the minimum detectable; the upper limit of detection was 10000, thus > 10000 indicates the count was higher than the maximum detectable]

A treatment strength of 0.3g/L and 0.4g/L produced a reduction in some bacteria within the time period of this test. Treatment was effective against all bacteria tested at 0.5g/L and above.

Example 3

Protocol for treatment of 80 litres sewage in 100 litre on-board sewage treatment tank litre of fresh water to form a treatment solution.

This treatment solution is added to 80 litres of raw human sewage in a 100 litre sewage treatment tank. The mixture is agitated with a motor-driven impeller operating at 5 revolutions per minute for a period of 20 minutes.

After treatment, the treated sewage is ready for discharge from the tank into the sea.

Example 4

Protocol for treatment of 80 litres sewage in 100 litre on-board sewage treatment tank (No impeller).

A revised protocol was devised for sewage treatment in which vessel movement provides agitation of the sewage being treated.

100g of pentapotassium bis (peroxy monosulphate) bis (sulphate) is combined with 200ml_ litre of fresh water and the solution added to 80 litres of untreated human sewage in a sewage treatment tank. The tank is vented to the atmosphere and is then sealed.

The mixture is left to incubate for an hour, the tank contents being mixed by the ship's movement during passage. After this period, the tank contents are ready for discharge into the sea.

The present invention thus provides treatment of sewage on-board boats and ships and compositions for use in sewage treatment.