PA DEPT OF AGRICULTURE: NUTRIENTS.

Objective:

Pennsylvania Department of Agriculture engaged INTAG’s Department of Applied Sciences to conduct a study on the use of INTAG patented bioreactors to process agro-industrial waste streams, such as aquaculture sludge, poultry manure, and restaurant pre/post-consumer waste into usable plant growth nutrients for application in hydroponic and field cultivation systems.

Outcome:

Focusing primarily on processing biodigestate waste from small-batch restaurant digesters, INTAG found that sludge produced from pre/post-consumer food waste can adequately be converted into bioavailable nutrient solution for cultivating crops in a hydroponic setting, if the pH of the input digestate is adjusted prior to introduction into INTAG patented bioreactors, as the pH of the input digestate was 3.9. This resulted in the rise of a secondary focus for this study, which looked at methods for manipulating the pH of the influent without negatively impacting the performance of the INTAG bioreactors. INTAG found that the safest methods for adjusting the pH of the influent digestate were to use either chemical lime or limestone pretreatments. Other methods of adjusting pH, such as dosing Sodium-bicarbonate, were found to increase trace minerals, such as sodium, that could negatively impact the performance of the INTAG bioreactors, and/or the health of the plants being cultivated from the resulting effluent.

Background:

INTAG’s aerobic bioreactor is a system for treating agroindustrial waste streams such as aquaculture sludge, animal manures, human sewage sludge, biodigestate, and the associated chemical wastes; ammonia, nitrite, nitrate, and phosphorous, particularly phosphates.

While biodigestion systems can be utilized to process a wide range of waste streams, from sewage to animal offal, INTAG has focused much of its efforts on addressing biodigestion of agro-industrial waste streams, particularly animal waste sludge from intensive farming operations. The United States Environmental Protection Agency (EPA) notes that anaerobic biodigestion is particularly beneficial to farms with a minimal cattle herd of 500 head, or an of hogs, 2,000 head, where the manure management scheme involves the use of anaerobic lagoons or deep pits. Furthermore, the EPA recommends anaerobic digesters be implemented if at least 90% of the waste produced from these farms is collected regularly, and where the waste is primarily slurry manure or semi-solid manure.

While aerobic digestion has been shown to have increased mineralization performance over anaerobic digestion, much of the previous research conducted on biodigesting agro-industrial wastes has focused on anaerobic digesters, as prior to the development of the INTAG bioreactor, there were few suitable aerobic digestion methods. INTAG’s patented aerobic bioreactor process fills this niche, providing a single-stage method by which to break down suspended solids and mineralize the nutrients found in waste sludge.

One of the key reasons that INTAG aerobic bioreactors are advantageous to anaerobic units currently being tested for sludge remediation, is the impact that pH has on the ability for digesters to efficiently break down sludge. University testing has shown that as pH dropped below 6.5, the anaerobic processes slowed. Below pH 6.0, methanogen activity was inhibited. The higher pH requirements of anaerobic digesters to properly break down sludge negatively impacts the ability to discharge digestate back into a growing system without being properly pre-treated.

Operating at a pH 6.4-6.8, INTAG’s aerobic bioreactor beds have shown the ability to efficiently mineralize key nutrients found in aquaculture sludge, aligning with research conducted by Conroy and Courtier that shows that decreases in pH facilitated the mineralization of macro and microelements in fish sludge. Due to the ability of INTAG bioreactors to operate in a pH range similar to the desired pH of plant growing solution, nutrient-rich discharge water from INTAG bioreactors can be seamlessly reintroduced into plant growing equipment.

In addition to variability in pH, research has found that incorporating discharge from anaerobic digesters back into an aquaponic system is complicated by the increased levels of Total Solids (TS), Chemical Oxygen Demand (COD), Volatile Fatty Acids (VFA), Total Ammonia Nitrogen (TAN), and other phytotoxic anaerobic secondary metabolites, compared to levels found in aerobic processes, such as INTAG’s patented bioreactor process.

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