NUTRIENT RECOVERY AND USE

Notice of Government-Sponsored Research

This invention was made with Government support under grant contract number RD835569 awarded by the National Science Foundation. The Government has certain rights in the invention.

Cross-Reference to Related Application

This application claims priority to co-pending U.S. Provisional Application Serial Number 62/365,729, filed July 22, 2016, which is hereby incorporated by reference herein in its entirety.

Background

Although wastewater is commonly viewed as a problematic "waste" stream, it often contains large amounts of compounds that could be put to beneficial use. For example, residential wastewater is an abundant source of nutrients, such as nitrogen, phosphorous, and potassium. These nutrients are major components of synthetic fertilizers typically used in agricultural and horticultural applications. If such nutrients could be economically harvested from wastewater and made available to end users at low cost, they could be of great benefit to those end users, particularly in arid regions where poor soil conditions exist.

Wastewater is typically treated before being released to the environment as untreated wastewater can cause environmental degradation. For example, wastewater is often treated in wastewater treatment (WWT) plants to remove its organic compounds and nutrients. The organic compounds are typically removed using biological processes, while the nutrients are removed through additional process operations. Nutrient removal processes impose additional costs. Additionally, nutrients that are removed through these operations become unavailable for use in agricultural or horticultural processes.

Existing methods for the recovery and reuse of nutrients from wastewater have inherent drawbacks. Precipitation-based approaches, such as the formation of magnesium ammonium phosphate (struvite) and calcium phosphate, often require elevated pH, high nutrient concentrations, addition of additional chemicals (e.g., magnesium oxide), subsequent dewatering and drying, and handling/packaging, which adds to the costs. Another approach is the direct use of partially-treated and disinfected wastewater for plant irrigation without prior removal of nutrients (direct fertigation). Such methods are appealing since the nutrients are preserved in the irrigation water and utilized efficiently. However, direct fertigation requires that the demand (i.e., end user) be physically located near the supply (wastewater source). This is something that is often not possible or practical.

In view of the above discussion, it can be appreciated that it would be desirable to have a low-cost system and method for recovering nutrients from nutrient sources, such as a wastewater, and making such nutrients available to end users in agricultural or horticultural processes.

Brief Description of the Drawings

The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, which are not necessarily drawn to scale.

Fig. 1 is a block diagram of an embodiment of a system for nutrient recovery and use.

Fig. 2A is a side view of an embodiment of a nutrient cartridge that can be used in the system of Fig. 1 , the cartridge being shown during a nutrient charging process.

Fig. 2B is a side view of the nutrient cartridge of Fig. 2, the cartridge being shown during a nutrient discharging process.

Fig. 3 is a side view of an alternative embodiment of a nutrient cartridge that can be used in the system of Fig. 1 , the cartridge being configured for vertical upflow.

Fig. 4 is a side view of a further alternative embodiment of a nutrient cartridge that can be used in the system of Fig. 1 , the cartridge comprising multiple individually removable modules that can have alternative configurations.

Fig. 5 is a side view of an embodiment of a nutrient cartridge that can be used in the system of Fig. 1 , the cartridge including an indicator that indicates a level of charge within the cartridge.

Fig. 6 is a side view of an embodiment of a nutrient cartridge that incorporates aeration. Detailed Description

As described above, it would be desirable to have a low-cost system and method for recovering nutrients from nutrient sources, such as a wastewater, and making such nutrients available to end users in agricultural or horticultural processes. Disclosed herein are examples of such systems and methods. In one embodiment, a system comprises reusable nutrient cartridges that are configured to adsorb nutrients from a nutrient stream and then used at an agricultural or horticultural site as a fertilizer source. In some embodiments, the cartridges can be "charged" with nutrients at a nutrient source site by flowing a nutrient stream through the cartridge, delivered to an end use site, used to fertilize crops or other plants at the end use site by flowing water through the charged cartridge (thereby "discharging" the cartridge), and then returned to the nutrient source site for recharging. The cartridge can then be reused in this manner again and again until the end of its useful life. Although the system is scalable, in some embodiments, the cartridges are relatively small in size so as to facilitate easy delivery to the end use site, which may be remote from the nutrient source site.

In the following disclosure, various specific embodiments are described. It is to be understood that those embodiments are example implementations of the disclosed inventions and that alternative embodiments are possible. All such embodiments are intended to fall within the scope of this disclosure.

Disclosed herein are nutrient recovery systems employing compact, reusable nutrient cartridges capable of capturing nutrients from nutrient streams and subsequently releasing them in desired, targeted streams. The cartridges utilize ion exchange and adsorptive materials to selectively capture pertinent nutrient material from the nutrient streams, thereby providing a method for low-cost nutrient removal. The cartridges, once charged with nutrient material, subsequently release nutrients where desired serving as a passive, low-cost technology for nutrient removal and fertigation. The cartridges house ion exchange and adsorptive media in combination with filter material to achieve a flow-through design. In some embodiments, an indicator is used to indicate the level of nutrient charge (i.e., nutrient concentration) within the cartridge. Consequently, the disclosed systems enable passive nutrient recovery, effectively alleviating problems associated with the lack of access to pertinent nutrient resources necessary for remote agricultural operations in non-ideal locations.

Fig. 1 provides an overview of an example nutrient recovery and use system 10.

As indicated in the figure, the system 10 includes a nutrient source 12 that can produce an aqueous nutrient stream from which nutrients can be collected. The nutrient source 12 can comprise any source that generates a nutrient stream. For example, the nutrient source 12 can be a wastewater treatment facility. In other cases, the nutrient source 12 can be a septic system or sewer line of one or a number of homes. In still other cases, the nutrient source 12 can be one or a number of homes that collect urine separate from other human waste (e.g., using urinals). In further cases, the nutrient source 12 can be a source of food waste. Other examples of potential nutrient sources 12 are fish ponds and aquaculture tanks. Notably, the specific nature of the nutrient source 12 is not critical. More important is that the source 12 generates an aqueous nutrient stream from which nutrients can be collected.

With further reference to Fig. 1 , a nutrient stream from the nutrient source 12 can be provided to a reusable nutrient cartridge 14. In some embodiments, the nutrient stream has low suspended solids concentrations, low pathogenic materials, and high nutrient concentrations (specifically nitrogen in the form of urea or ammonia, phosphorous, and/or potassium). The nutrient stream can be flowed through the nutrient cartridge 14, which utilizes a specific blend of ion exchange, biological, and/or adsorptive materials to selectively capture nutrients from the nutrient stream. In some embodiments, the cartridge is placed in-line of the flowing stream to facilitate the removal of the nutrient materials in a process that resembles the operation of an inline filter. As the nutrient stream is flowed through the cartridge 14, the cartridge adsorbs the nutrients so as to become "charged" with the nutrients. Once the cartridge 14 reaches its nutrient capture capacity, it is deemed to be fully charged and is prepared for use as a source of fertilizer.

At that point, the reusable nutrient cartridge 14 can be delivered to an end use site 18 at which it will be "discharged." Such discharging comprises flowing water through the cartridge 14 to release the nutrients contained in the cartridge and produce a dilute nutrient solution that can be used to simultaneously irrigate and fertilize, or fertigate, crops or other plants. This process is illustrated in Fig. 1 with a further reusable nutrient cartridge 16 located at the end use site 18. In some embodiments, the water comprises clean water containing no additives. In other embodiments, the water can comprise compounds that assist in the release of nutrients from the cartridge 16 and/or compounds, such as specific nutrients, that the end user wishes to provide to the crops or other plants. In still other embodiments, additional physical, chemical, or biological processes can be performed at the end use site 18 to induce the discharge of the nutrients. Such processes can comprise one or more of manipulation of concentration gradients, biological regeneration, precipitation and dissolution, ion exchange, electrochemical oxidation, thermal stimulation, and ultrasonic irradiation. Regardless, discharging entails creating conditions to reverse the fugacity gradient to release the bound nutrient materials into the aqueous stream or to oxidize them completely so as to achieve removal, thus regenerating the capacity to be charged again. During ideal discharge scenarios, nutrients release into the flow-through stream for fertigation of any properly sized agricultural or horticultural operation.

Completing the discharge phase readies the reusable nutrient cartridge 16 for a new charging phase. Accordingly, once the cartridge 16 has been fully discharged at the end use site 18, it is ready for another charge cycle and can be returned to the nutrient source 12 for this purpose. The above-described cycle can be repeatedly performed throughout the useful life of the cartridge 14, 16.

The nutrient source 12 and the end use site 18 may be remote of each other. For this reason, the reusable nutrient cartridges 14, 16 can be relatively small to enable them to be easily delivered between the nutrient source 12 and the end use site 18. By way of example, the cartridges 14, 16 can have a volumetric capacity of approximately 1 to 5 L. In such cases, a variety of distribution method is possible, including delivery by land vehicle as well as by unmanned aerial vehicles (UAVs). It is noted, however, that the nutrient source 12 and the end use site 18 may be located close to each other, and even at the same site. For example, the nutrient source 12 could be located at one's home and the end use site could be a yard or greenhouse of the home. In such cases, the cartridge 14, 16 can be a fixed installation, in which case delivery is unnecessary. In that scenario, the cartridge 14, 16 could be submerged in a reservoir where the nutrients accumulate (e.g., septic tank, fish pond, aquaculture tank, or storm water retention pond), thus providing a nutrient sink.

Figs. 2A and 2B show an example reusable nutrient cartridge 20. The cartridge 20 is illustrated in Fig. 2A during the charging phase, while the cartridge is illustrated in Fig. 2B during the discharging phase. As shown in the figures, the cartridge 20 includes an outer housing 22 that contains nutrient adsorption material 24 that is configured to capture nutrients contained within the nutrient stream. In some embodiments, the nutrient adsorption material 24 comprises zeolitic materials (zeolites) in either granular or solidified powder form. In some embodiments the nutrient adsorption material 24 can comprise other materials that assist in the removal of dissolved organic compounds from the nutrient stream. For example, the nutrient adsorption material 24 can also include pyrolyzed forms of carbon, such as biochar, charcoal, and/or granular activated carbon to remove compounds that contribute to color and odor. Various other mineral rocks, such as calcium and magnesium carbonates and volcanic rock, can also be used as adsorbents, bio carriers, and struvite precipitation sites. Ordinary Portland cement (OPC) can be utilized as a binding material to form a composite material for simultaneous removal of various materials. The ideal mixture is one that is capable of removing high quantities of pertinent nutrient materials from the influent nutrient stream. Pathogen removal can also be achieved by the utilization of microfiltration technology, which can passively degrade unwanted bacteria and pathogenic materials. The characteristics of the nutrient adsorption material 24, such as material composition, ratio of material mixtures, particle size, porosity, permeability, hydrophilicity, and hydrophobicity, can influence the performance of the cartridge 20 and the effectiveness of the intended objective of recovering nutrients.

As shown in Fig. 2A, the reusable nutrient cartridge 20 is charged by flowing the nutrient stream through an inlet 26 at one end of the cartridge, through the nutrient adsorption material 24, and out through an outlet 28 at the opposite end of the cartridge. As is further shown in Fig. 2A, mesh 30 can be provided at one or both of the inlet 26 and outlet 28 to retain the nutrient adsorption material 24 within the housing 22. As the nutrient stream is flowed through the nutrient adsorption material 24, the material collects nutrients, as indicated by the shading in the figure. At least initially, clean water (i.e., water stripped of its nutrients) flows out from the outlet 28. Notably, the nutrient stream can flow through the nutrient adsorption material 24 via capillary movement. This capability accommodates operation of the cartridge in microgravity environments making the device a suitable technology for space exploration and Mars colonization missions. The capillary movement can be enhanced, if desired, by utilizing hydrophilic media within the nutrient adsorption material 24. In other embodiments, hydrophobic materials can be utilized to enhance the performance of the reusable nutrient cartridge 20. For example, hydrophobic media can be used to create better contact between the nutrient stream and sorbents in the nutrient adsorption material 24. Hydrophobic or hydrophilic surfaces may either be made available through native material properties (such as polytetrafluoroethylene (PTFE)) or through surface modification through the use of femto lasers.

With reference to Fig. 2B, a charged reusable nutrient cartridge 20 can be discharged by flowing clean water through the cartridge so as to produce a dilute nutrient solution that exits the cartridge via the outlet 28. As noted above, however, the water flowed through the cartridge 20 can comprise additives that either assist with the uptake of nutrients or provide some benefit to the crops or other plants receiving the solution.

Fig. 3 illustrates an alternative configuration for a reusable nutrient cartridge 32. Like the cartridge 20, the cartridge 32 includes an outer housing 34 that contains nutrient adsorption material 36. In addition, the housing 34 includes an inlet 38 for receiving a nutrient stream and an outlet 40 from which a dilute nutrient solution can flow. In this configuration, however, the inlet 38 and outlet 40 are both located at the same end (i.e., top end) of the housing 34 and the nutrient stream is released at the bottom of the cartridge 32 using a conduit 41 such that the stream flows upward through the cartridge before exiting the cartridge.

Fig. 4 illustrates a further alternative configuration for a reusable nutrient cartridge 42. This cartridge 42 also includes an outer housing 44 having an inlet 46 and an outlet 48. In this configuration, however, the cartridge 42 comprises multiple individually removable/replaceable modules 50 each contain material through which the nutrient stream flows. In some embodiments, each module 50 comprises different materials that are either specifically configured to remove a particular material (e.g., nutrient) from a nutrient stream during charging or add a particular compound (e.g., nutrient) to the nutrient solution during discharging. This configuration enables specialization of the cartridge for optimal performance based on location and application. As an example, one or more of the modules 50 can be configured to uptake nutrients while one or more other modules 50 can be configured to "polish" the stream by removing color, turbidity, and/or pathogens. In some embodiments, the reusable nutrient cartridge can include a charge indicator that provides an indication of the level of nutrient concentration within the cartridge. Fig. 5 shows an example of this. As illustrated in this figure, a cartridge 52 includes a housing 54 having an inlet 56 and an outlet 58. Contained within the housing 54 is nutrient-adsorbing material 60. Mounted to the exterior of the housing 54 is an indicator 61 , in the form of a gauge, which identifies the level of charge within the container 52. In the example of Fig. 5, the level of charge is determined by measuring the potential difference between an anode 62 provided at one end of the cartridge 52 and a cathode 64 provided at the other end of the cartridge. In such an embodiment, the potential difference can be correlated to a concentration of nutrient ions within the cartridge 52. Notably, both the indicator 61 and the charge quantification method can take different forms. For example, the indicator 61 can be configured as a liquid crystal status bar or battery similar to that used in mobile phones, or a series of light emitting diodes (LEDs) similar to those used on laptop batteries. The technology used to measure the level of charge can alternatively operate based upon total dissolved solids, ammonium concentration, pH, electric potential, or other suitable measure.

Fig. 6 illustrates a further example nutrient cartridge 66. As before, the cartridge 66 includes a housing 68 having an inlet 70 and an outlet 72, and contains nutrient- adsorbing material 74. A nutrient stream can be fed to the inlet 70 from a nutrient source 76 using a pump 78. In this case, aeration is used to assist with nitrification. In particular, air is pumped into the cartridge 66 using an air pump 80. The air flows from the pump 80 through a conduit 82 to a membrane diffuser 84 that extends along the interior of the housing 68 from the bottom to the top of the nutrient-adsorbing material 74. The flow of air through the nutrient-adsorbing material 74 provides both oxygen and turbulence that can facilitate nutrient capture and release processes. Such a configuration may be particularly useful in situations in which the nutrient source 76 is collocated with the end user site.