Bioaugmentation of Overloaded Anaerobic Digesters Restores Function and Archaeal Community

Adding beneficial microorganisms to anaerobic digesters for improved performance (i.e. bioaugmentation) has been shown to decrease recovery time after organic overload or toxicity upset. Compared to strictly anaerobic cultures, adding aerotolerant methanogenic cultures may be more practical since they exhibit higher methanogenic activity and can be easily dried and stored in ambient air for future shipping and use. In this study, anaerobic digesters were bioaugmented with both anaerobic and aerated, methanogenic propionate enrichment cultures after a transient organic overload. Digesters bioaugmented with anaerobic and moderately aerated cultures recovered 25 and 100 days before non-bioaugmented digesters, respectively. Increased methane production due to bioaugmentation continued a long time, with 50–120% increases 6 to 12 SRTs (60–120 days) after overload. In contrast to the anaerobic enrichment, the aerated enrichments were more effective as bioaugmentation cultures, resulting in faster recovery of upset digester methane and COD removal rates. Sixty days after overload, the bioaugmented digester archaeal community was not shifted, but was restored to one similar to the pre-overload community. In contrast, non-bioaugmented digester archaeal communities before and after overload were significantly different. Organisms most similar to Methanospirillum hungatei had higher relative abundance in well-operating, undisturbed and bioaugmented digesters, whereas organisms similar to Methanolinea tarda were more abundant in upset, non-bioaugmented digesters. Bioaugmentation is a beneficial approach to increase digester recovery rate after transient organic overload events. Moderately aerated, methanogenic propionate enrichment cultures were more beneficial augments than a strictly anaerobic enrichment

Influent Wastewater Microbiota and Temperature Influence Anaerobic Membrane Bioreactor Microbial Community

Sustainable municipal wastewater recovery scenarios highlight benefits of anaerobic membrane bioreactors (AnMBRs). However, influences of continuous seeding by influent wastewater and temperature on attached-growth AnMBRs are not well understood. In this study, four bench-scale AnMBR operated at 10 and 25 °C were fed synthetic (SPE) and then real (PE) primary effluent municipal wastewater. Illumina sequencing revealed different bacterial communities in each AnMBR in response to temperature and bioreactor configuration, whereas differences were not observed in archaeal communities. Activity assays revealed hydrogenotrophic methanogenesis was the dominant methanogenic pathway at 10 °C. The significant relative abundance of Methanosaeta at 10 °C concomitant with low acetoclastic methanogenic activity may indicate possible Methanosaeta-Geobacter direct interspecies electron transfer. When AnMBR feed was changed to PE, continual seeding with wastewater microbiota caused AnMBR microbial communities to shift, becoming more similar to PE microbiota. Therefore, influent wastewater microbiota, temperature and reactor configuration influenced the AnMBR microbial community

Autocatalytic Pyrolysis of Wastewater Biosolids for Product Upgrading

The main goals for sustainable water resource recovery include maximizing energy generation, minimizing adverse environmental impacts, and recovering beneficial resources. Wastewater biosolids pyrolysis is a promising technology that could help facilities reach these goals because it produces biochar that is a valuable soil amendment as well as bio-oil and pyrolysis gas (py-gas) that can be used for energy. The raw bio-oil, however, is corrosive; therefore, employing it as fuel is challenging using standard equipment. A novel pyrolysis process using wastewater biosolids-derived biochar (WB-biochar) as a catalyst was investigated to decrease bio-oil and increase py-gas yield for easier energy recovery. WB-biochar catalyst increased the py-gas yield nearly 2-fold, while decreasing bio-oil production. The catalyzed bio-oil also contained fewer constituents based on GC-MS and GC-FID analyses. The energy shifted from bio-oil to py-gas, indicating the potential for easier on-site energy recovery using the relatively clean py-gas. The metals contained in wastewater biosolids played an important role in upgrading pyrolysis products. The Ca and Fe in WB-biochar reduced bio-oil yield and increased py-gas yield. The py-gas energy increase may be especially useful at water resource recovery facilities that already combust anaerobic digester biogas for energy since it may be possible to blend biogas and py-gas for combined use

Quantitative Detection of Syntrophic Fatty Acid-degrading Bacterial Communities in Methanogenic Environments

In methanogenic habitats, volatile fatty acids (VFA), such as propionate and butyrate, are major intermediates in organic matter degradation. VFA are further metabolized to H2, acetate and CO2 by syntrophic fatty acid-degrading bacteria (SFAB) in association with methanogenic archaea. Despite their indispensable role in VFA degradation, little is known about SFAB abundance and their environmental distribution. To facilitate ecological studies, we developed four novel genus-specific quantitative PCR (qPCR) assays, with primer sets targeting known SFAB: Syntrophobacter, Smithella, Pelotomaculum and Syntrophomonas. Primer set specificity was confirmed using in silico and experimental (target controls, clone libraries and melt-curve analysis) approaches. These qPCR assays were applied to quantify SFAB in a variety of mesophilic methanogenic habitats, including a laboratory propionate enrichment culture, pilotand full-scale anaerobic reactors, cow rumen, horse faeces, an experimental rice paddy soil, a bog stream and swamp sediments. The highest SFAB 16S rRNA gene copy numbers were found in the propionate enrichment culture and anaerobic reactors, followed by the bog stream and swamp sediment samples. In addition, it was observed that SFAB and methanogen abundance varied with reactor configuration and substrate identity. To our knowledge, this research represents the first comprehensive study to quantify SFAB in methanogenic habitats using qPCR-based methods. These molecular tools will help investigators better understand syntrophic microbial communities in engineered and natural environments

Pyrolysis of Wastewater Biosolids Significantly Reduces Estrogenicity

Most wastewater treatment processes are not specifically designed to remove micropollutants. Many micropollutants are hydrophobic so they remain in the biosolids and are discharged to the environment through land-application of biosolids. Micropollutants encompass a broad range of organic chemicals, including estrogenic compounds (natural and synthetic) that reside in the environment, a.k.a. environmental estrogens. Public concern over land application of biosolids stemming from the occurrence of micropollutants hampers the value of biosolids which are important to wastewater treatment plants as a valuable by-product. This research evaluated pyrolysis, the partial decomposition of organic material in an oxygen-deprived system under high temperatures, as a biosolids treatment process that could remove estrogenic compounds from solids while producing a less hormonally active biochar for soil amendment. The estrogenicity, measured in estradiol equivalents (EEQ) by the yeast estrogen screen (YES) assay, of pyrolyzed biosolids was compared to primary and anaerobically digested biosolids. The estrogenic responses from primary solids and anaerobically digested solids were not statistically significantly different, but pyrolysis of anaerobically digested solids resulted in a significant reduction in EEQ; increasing pyrolysis temperature from 100 °C to 500 °C increased the removal of EEQ with greater than 95% removal occurring at or above 400 °C. This research demonstrates that biosolids treatment with pyrolysis would substantially decrease (removal \u3e 95%) the estrogens associated with this biosolids product. Thus, pyrolysis of biosolids can be used to produce a valuable soil amendment product, biochar, that minimizes discharge of estrogens to the environment

Anaerobic Digester Bioaugmentation Influences Quasi Steady State Performance and Microbial Community

Nine anaerobic digesters, each seeded with biomass from a different source, were operated identically and their quasi steady state function was compared. Subsequently, digesters were bioaugmented with a methanogenic culture previously shown to increase specific methanogenic activity. Before bioaugmentation, different seed biomass resulted in different quasi steady state function, with digesters clustering into three groups distinguished by methane (CH4) production. Digesters with similar functional performance contained similar archaeal communities based on clustering of Illumina sequence data of the V4V5 region of the 16S rRNA gene. High CH4 production correlated with neutral pH and high Methanosarcina abundance, whereas low CH4production correlated to low pH as well as high Methanobacterium and DHVEG 6 family abundance. After bioaugmentation, CH4 production from the high CH4 producing digesters transiently increased by 11 ± 3% relative to non-bioaugmented controls (p \u3c 0.05, n = 3), whereas no functional changes were observed for medium and low CH4producing digesters that all had pH higher than 6.7. The CH4 production increase after bioaugmentation was correlated to increased relative abundance of Methanosaeta and Methaospirillum originating from the bioaugment culture. In conclusion, different anaerobic digester seed biomass can result in different quasi steady state CH4production, SCOD removal, pH and effluent VFA concentration in the timeframe studied. The bioaugmentation employed can result in a period of increased methane production. Future research should address extending the period of increased CH4 production by employing pH and VFA control concomitant with bioaugmentation, developing improved bioaugments, or employing a membrane bioreactor to retain the bioaugment

Ion Exchange-Precipitation for Nutrient Recovery from Dilute Wastewater

Regulated phosphorus (P) and nitrogen (N) discharges and the cost of fertilizer provide economic drivers for nutrient removal and recovery from wastewater. This study used ion exchange (IX) in dilute (domestic) wastewater to concentrate nutrients with subsequent recovery by struvite precipitation. This is the first tertiary wastewater treatment study directly comparing P removal using a range of Fe, Cu, and Al-based media followed by clinoptilolite IX columns for N removal and precipitation using the combined regenerants. Phosphate removal prior to breakthrough was 0.5–2.0 g P Lmedia−1, providing effluent concentrations −1 PO4-P and −1 NH4-N for ≥80 bed volumes. Dow-FeCu resin provided effective P removal, efficient neutral pH regeneration and 560 mg P L−1 in the regeneration eluate (≥100× concentration factor). Exchange capacity of clinoptilolite in column mode was 3.9–6.1 g N Lmedia−1 prior to breakthrough. Precipitation using the combined cation and anion regenerants resulted in a maximum of 74% P removal using Dow-FeCu. Precipitates contained impurities, including Al3+, Ca2+, and Fe. Overall, the IX-precipitation recovery process removed ≥98% P and 95% N and precipitates contained 13% P and 1.6% N. This sequential process can satisfy increasingly stringent wastewater standards and offers an effective alternative to traditional treatment technologies that simply remove nutrients. Approximately 84% of total P and 97% of total Kjeldahl N entering a treatment plant can be captured (accounting for primary clarifier removal), whereas most existing technologies target side streams that typically contain only 20–30% of influent P and 15–20% of influent N

Pyrolysis of Dried Wastewater Biosolids Can Be Energy Positive

Pyrolysis is a thermal process that converts biosolids into biochar (a soil amendment), py-oil and py-gas, which can be energy sources. The objectives of this research were to determine the product yield of dried biosolids during pyrolysis and the energy requirements of pyrolysis. Bench-scale experiments revealed that temperature increases up to 500 °C substantially decreased the fraction of biochar and increased the fraction of py-oil. Py-gas yield increased above 500 °C. The energy required for pyrolysis was approximately 5-fold less than the energy required to dry biosolids (depending on biosolids moisture content), indicating that, if a utility already uses energy to dry biosolids, then pyrolysis does not require a substantial amount of energy. However, if a utility produces wet biosolids, then implementing pyrolysis may be costly because of the energy required to dry the biosolids. The energy content of py-gas and py-oil was always greater than the energy required for pyrolysis

Bioaugmentation for Improved Recovery of Anaerobic Digesters After Toxicant Exposure

Bioaugmentation was investigated as a method to decrease the recovery period of anaerobic digesters exposed to a transient toxic event. Two sets of laboratory-scale digesters (SRT = 10 days, OLR = 2 g COD/L-day), started with inoculum from a digester stabilizing synthetic municipal wastewater solids (MW) and synthetic industrial wastewater (WW), respectively, were transiently exposed to the model toxicant, oxygen. Bioaugmented digesters received 1.2 g VSS/L-day of an H2-utilizing culture for which the archaeal community was analyzed. Soon after oxygen exposure, the bioaugmented digesters produced 25–60% more methane than non-bioaugmented controls (p \u3c 0.05). One set of digesters produced lingering high propionate concentrations, and bioaugmentation resulted in significantly shorter recovery periods. The second set of digesters did not display lingering propionate, and bioaugmented digesters recovered at the same time as non-bioaugmented controls. The difference in the effect of bioaugmentation on recovery may be due to differences between microbial communities of the digester inocula originally employed. In conclusion, bioaugmentation with an H2-utilizing culture is a potential tool to decrease the recovery period, decrease propionate concentration, and increase biogas production of some anaerobic digesters after a toxic event. Digesters already containing rapidly adaptable microbial communities may not benefit from bioaugmentation, whereas other digesters with poorly adaptable microbial communities may benefit greatly

Relating Anaerobic Digestion Microbial Community and Process Function

Anaerobic digestion (AD) involves a consortium of microorganisms that convert substrates into biogas containing methane for renewable energy. The technology has suffered from the perception of being periodically unstable due to limited understanding of the relationship between microbial community structure and function. The emphasis of this review is to describe microbial communities in digesters and quantitative and qualitative relationships between community structure and digester function. Progress has been made in the past few decades to identify key microorganisms influencing AD. Yet, more work is required to realize robust, quantitative relationships between microbial community structure and functions such as methane production rate and resilience after perturbations. Other promising areas of research for improved AD may include methods to increase/control (1) hydrolysis rate, (2) direct interspecies electron transfer to methanogens, (3) community structure–function relationships of methanogens, (4) methanogenesis via acetate oxidation, and (5) bioaugmentation to study community–activity relationships or improve engineered bioprocesses