Progress 07/01/21 to 02/28/22

Outputs
Target Audience: Nothing Reported Changes/Problems:The original vision for the use of the hydrogel technology evaluated was that it might have potential application in a number of streams of direct interest to AES, primarily in the agricultural and wetland application segment. The testing completed revealed that only in applications of low P level streams would these hydrogels in their current state, be a possible aid, such as in improving the efficiency of constructed wetlands at removing phosphorus loads. However, before this could be pursued further, the completed program identified several techno-economic questions that must be answered, such as: Why there was a significant difference in performance observed between the initial assessment of the materials and the current generation? (See Figure 7 and Table 4) What is causing the degradation of the current hydrogel materials? The original evaluation completed in 2020 did not exhibit this response, even after multiple runs with a fresh charge of wastewater with the same batch of material. What is the composition of the degraded material? If the degradation releases the phosphorus absorbed, where does this go (back into the stream or as a settled material?) As noted in the conclusions, an estimate of the operating costs could not be determined since the "final" composition of the hydrogels could not be determined in order to assess the amount of material required to treat a given application. The degradation aspect also raises the question on how to contain or package the hydrogels in a given application. Based on these primary concerns, AES has determined that the current state of the hydrogel technology requires additional fundamental investigation before advancing to commercialization. Consequently, it has determined that while the potential exists for some limited application, AES will not be pursuing a Phase 2 SBIR application. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Initial testing was conducted in Stage 2 to confirm the phosphorus reduction results observed in September 2020 using hydrogels. These tests were repeated using the same waste stream from an EBO. Phosphorus reduction (27%-37%, TP-OP, respectively) was reported to be significantly less than what was originally observed last year (93% OP reduction). Various hydrogel shapes, feedstock material, and reactor loading methods were tested to repeat the phosphorus reduction previously seen. Variables tested in hydrogel preparation method and reactor loading method did not have a significant impact on phosphorus reduction. The gels were then tested on a swine stream instead of the stream from the EBO, and results were more aligned with what was originally seen. OP reduction in the swine stream was 95%. In both cases of the poultry and swine streams tested, the hydrogels were discolored and seemed to break down into a black sludge-like material, although the degradation in the swine stream was more drastic. Along with discoloration of the hydrogels themselves, the streams in which the hydrogels were submerged were also darkened and discolored. After concluding that hydrogel performance was impacted by stream characteristic rather than hydrogel preparation or reactor loading methods, a baseline hydrogel was determined for further testing. Various waste streams were tested to observe the impact on phosphorus recovery and degradation. Two swine streams (medium P load and low P load) and one mixed swine and dairy digestate stream (high P load) were originally tested. In the medium loaded swine stream and high loaded digestate stream, the hydrogels removed nearly all of the orthophosphate. After these tests, the gels were completely broken down and dark in color in the medium loaded stream, and moderately degraded and dark in color in the digestate stream. Hydrogels were only able to remove 54% of the OP from the low loaded swine stream, and interestingly there was a lesser degree of hydrogel degradation seen after testing. The effect of ammonia on hydrogel degradation was also tested by reducing the ammonia from the medium loaded swine stream before testing. OP recovery was similar to what was reported in studies on the stream without ammonia reduction. Breakdown of the gels after testing was also similar between studies with and without ammonia reduction. In this brief study, it was concluded that ammonia load in the waste stream does not affect the P recovery or degradation of the hydrogels. The hydrogels were also tested on two dairy streams: a high loaded P stream, and a low loaded P stream. It was hypothesized that a component of the typical swine diet could be causing the hydrogels to break down by complexing with the iron coating of the gels. In both cases, the gels seemed to hold their shape better throughout the tests compared to testing with swine streams, but there was still an extent of discoloration and break down. The high loaded stream was less discolored than the low loaded stream. The OP was nearly completely reduced in the low loaded stream, but only 37% OP reduction was observed in the high loaded stream. Of note, comparatively lower phosphorus recoveries are noted in cases where a lesser degree of degradation was observed. This was demonstrated in both swine manure samples and dairy manure samples. The best OP reduction seen in all tests was observed in the treatment of swine manure streams, although the most extreme degradation was also observed in swine manure tests. In addition to agricultural streams, a low-P surface water was also tested using hydrogels. The hydrogels achieved near total reduction of both TP and OP in the sample, however the initial P levels were extremely low to begin with. Hydrogels did not degrade in these tests. Results were encouraging and demonstrate that hydrogels have some potential to function in surface waters, although the overall capacity of the hydrogels in surface water could not be tested and results remain inconclusive due to the very low range of phosphorus that was observed throughout the test. In addition to the tests completed in the lab, it was envisioned to complete a long-term study of the hydrogels in the field. Reactors were installed at Coldwater Creek Wetland to observe media performance on a continuous basis. Due to several factors, including intake pump clogs, media blinding, power issues and low phosphorus levels in the wetland stream, it was decided to take the reactor system offline, and the long-term evaluation could not be conducted. Throughout the evaluation, hydrogels were tested alongside a phosphorus reducing pellet media. In the initial study in September 2020, the pellet media performed better than hydrogels in TP reduction, but the hydrogels appeared to be advantageous in reducing orthophosphate. In all cases where pellets were tested, a consistent performance was observed with the exception of tests on a high loaded dairy stream where scattered results were reported. Pellet material also held its shape and structure in all tests conducted using various waste streams and reactor conditions. The testing methods identified in Stage 1 work (conducted at BGSU) were based primarily on more passive static evaluations with a given water, whereas the work conducted in Stages 2 and 3 involved a more flowing water stream. Since the envisioned applications involved water flowing in some form, the methods employed in Stage 2 and 3 were considered more representative of field conditions. Stage 1 economics were limited in scope to components used to produce a given hydrogel composition. While the initial results from this analysis offered some potential positive direction, no definitive estimate of cost/gallon treated could be estimated due to unanswered questions on lower than expected performance and the impact of degradation. These unanswered questions must be reconciled first before a true estimate of material required to treat a given application can be answered. The degradation of hydrogels observed is perceived as a limiting factor that should be investigated further before the technology is ready for any field implementation. The following questions remain as challenges to be addressed moving forward: After hydrogel degradation, what is the composition of the degraded material? We were unable to address this question in the investigation because hydrogels were non-recoverable after testing. What is the mechanism that causes rapid degradation of the hydrogels? Various waste streams were investigated to assess the potential impact of agricultural diet and waste stream characteristics on hydrogel degradation. Although some observations were made on the "extent of degradation," broader conclusions could not be drawn to address this question.

Publications

Progress 07/01/21 to 02/28/22

Outputs
Target Audience: Nothing Reported Changes/Problems:Two main problems occured since startup: 1. In laboratory testing, the materials have not performed as originally provided. The primary cause for low performance has been related to rapid degradation in waters of interest. 2. Testing in the wetland application was not successful primarily due to high solids/contaminants entering the test unit preventing continuous flow operation of more than 16 hours. Laboratory testing of the water was successful suggesting the challenge faced was one of natural debris present in this application. Unfortunately, the wetland water supply is shutdown in October due to lower overall uptake in the wetland due to the transition to milder weather. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?Results have been shared primarily with technology provider (Bowling Green State University) and a high level overview of initial results shared with key stakeholder(s) in the area where work is being done. What do you plan to do during the next reporting period to accomplish the goals?We are approaching a decision point on a go/no go decision continuation with the technology. Emphasis is currently being placed to understand the degradation observed and possible lower cost alternatives to the primary component of the hydrogel (aginate).

Impacts
What was accomplished under these goals? Based on the work completed to date and our current understanding of the hydrogel technology, Table 4 reflects a high-level summary of hydrogel feasibility in the intended applications, with red, yellow, and green ratings reflecting hydrogel readiness for each application. Applications that are indicated red are deemed not feasibility for phosphorus reduction with hydrogels due to a combination of low performance and high degradation. Applications that are indicated yellow have shown some potential for phosphorus reduction with moderate degradation. With more work and understanding of the degradation mechanisms, swine and dairy applications could be feasible for hydrogel implementation. A green indication suggests that hydrogels are nearly ready for application. The only application that received a green rating was a Wetland application based on our results from Coldwater Creek. During these tests, the hydrogels held their shape and reduced phosphorus below detection limits of instrumentation. It should be noted though, that this was only demonstrated for a very low phosphorus load stream, so the green light rating is still limited to its application as a means of polishing low phosphorus loaded streams. Table 4: Feasibility of hydrogels for P reduction in intended applications Stream Type Phosphorus Load Readiness EBO Medium P Load Red Swine Medium P Load Yellow Swine Low P Load Yellow Swine/Dairy Digestate High P Load Red Dairy High P Load Yellow Dairy Low P Load Yellow Wetland Low P Load Green The degradation of hydrogels observed is perceived as a limiting factor that should be investigated further before the technology is ready for field implementation. The following questions remain as challenges to be addressed moving forward: After hydrogel degradation, what is the composition of the degraded material? We were unable to address this question in the investigation because hydrogels were non-recoverable after testing. What is the mechanism that causes rapid degradation of the hydrogels? Various waste streams were investigated to assess the potential impact of agricultural diet and waste stream characteristics on hydrogel degradation. Although some observations were made on the "extent of degradation," broader conclusions could not be drawn to address this question.

Publications