Kaushik Venkiteshwaran

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.

Meta-analysis of non-reactive phosphorus in water, wastewater, and sludge, and strategies to convert it for enhanced phosphorus removal and recovery

Current and future trends indicate that mining of natural phosphorus (P) reserves is occurring faster than natural geologic replenishment. This mobilization has not only led to P supply concerns, but has also polluted many of the worlds freshwater bodies and oceans. Recovery and reuse of this nuisance P offers a long-term solution simultaneously addressing mineral P accessibility and P-based pollution. Available physical, chemical, and biological P removal/recovery processes can achieve low total P (TP) concentrations (≤100 μg/L) and some processes can also recover P for direct reuse as fertilizers (e.g., struvite). However, as shown by our meta-analysis of over 20,000 data points on P quantity and P form, the P in water matrices is not always present in the reactive P (RP) form that is most amenable to recovery for direct reuse. Thus, strategies for removing and recovering other P fractions in water/wastewater are essential to provide environmental protection via P removal and also advance the circular P economy via P recovery. Specifically, conversion of non-reactive P (NRP) to the more readily removable/recoverable RP form may offer a feasible approach; however, extremely limited data on such applications currently exist. This review investigates the role of NRP in various water matrices; identifies NRP conversion mechanisms; and evaluates biological, physical, thermal, and chemical processes with potential to enhance P removal and recovery by converting the NRP to RP. This information provides critical insights into future research needs and technology advancements to enhance P removal and recovery.

Activity of methanogenic biomass after heat and freeze drying in air

It would be beneficial if methanogenic cultures could be preserved for anaerobic digester bioaugmentation or as seed for standard tests such as biochemical methane potential. However, storage of wet culture or drying in anaerobic atmosphere may not be economically feasible. In this study, the effect of heat and freeze drying in ambient air on the methanogenic activity of an anaerobic culture was determined. The anaerobic culture was dried in air at 104 °C for 12 h, and by freezing at −196 °C in air with subsequent drying at subzero temperatures. The rehydrated culture consistently produced CH4 from H2:CO2 and acetate after drying. Drying caused a greater decrease in acetate methanogenic activity compared to H2:CO2 methanogenic activity. Transcript qPCR results for a functional gene in methanogens (mcrA) also revealed significant survivability of rehydrated methanogenic populations. Inactivation due to drying differed among genera, with least to most inactivation in the order Methanospirillum < Methanosaeta < Methanoculleus.

Biochemical methane potential assays and anaerobic digester bioaugmentation using freeze dried biomass

In this study, freeze dried methanogenic biomass (FDMB) was used as inoculum in place of conventional, non-dried biomass for biochemical methane potential (BMP) assays and as a bioaugment to improve upset digester recovery. Methanogenic biomass was freeze dried and stored in an air atmosphere. Significant methanogenic activity was preserved in FDMB even with drying and storage in air; specific methanogenic activity (SMA) values were 65 ± 4.5% and 42 ± 10.4% for hydrogen:carbon dioxide (H2:CO2) and acetate, respectively, compared to non-dried biomass. There was no significant difference in BMP results for the four substrates tested (glucose, non-fat dry milk, thin stillage and dog food) when using FDMB and non-dried biomass as inocula. However, BMP assays using FDMB inocula took longer to complete. Methane (CH4) production from digesters exposed to a model toxicant (oxygen [O2]) recovered faster when bioaugmented with FDMB compared to digesters that received autoclaved biomass or no bioaugmentation. Methanogen communities in all digesters before toxicant exposure and bioaugmentation were similar. However, bioaugmented and non-augmented digester communities were significantly different during the recovery phase after toxicant exposure. Sequences similar to Methanospirillum were related to improved performance of the FDMB bioaugmented digesters. FDMB could be developed as a standard inoculum for BMP analyses and to bioaugment anaerobic digesters for improved performance. These results may encourage developing customized, dried methanogenic biomass for specific anaerobic biotechnology applications.

Phosphate removal and recovery using immobilized phosphate binding proteins

Progress towards a more circular phosphorus economy necessitates development of innovative water treatment systems which can reversibly remove inorganic phosphate (Pi) to ultra-low levels (<100 μg L−1), and subsequently recover the Pi for reuse. In this study, a novel approach using the high-affinity E. coli phosphate binding protein (PBP) as a reusable Pi bio-adsorbent was investigated. PBP was expressed, extracted, purified and immobilized on NHS-activated Sepharose beads. The resultant PBP beads were saturated with Pi and exposed to varying pH (pH 4.7 to 12.5) and temperatures (25–45 °C) to induce Pi release. Increase in temperature from 25 to 45 °C and pH conditions between 4.7 and 8.5 released less than 20% of adsorbed Pi. However, 62% and 86% of the adsorbed Pi was released at pH 11.4 and 12.5, respectively. Kinetic experiments showed that Pi desorption occurred nearly instantaneously (<5 min), regardless of pH conditions, which is advantageous for Pi recovery. Additionally, no loss in Pi adsorption or desorption capacity was observed when the PBP beads were exposed to 10 repeated cycles of adsorption/desorption using neutral and high pH (≥12.5) washes, respectively. The highest average Pi adsorption using the PBP beads was 83 ± 5%, with 89 ± 4.1% average desorption using pH 12.5 washes over 10 wash cycles at room temperature. Thermal shift assay of the PBP showed that the protein was structurally stable after 10 cycles, with statistically similar melting temperatures between pH 4 and 12.5. These results indicate that immobilized high-affinity PBP has the potential to be an effective and reversible bio-adsorbent suitable for Pi recovery from water/wastewater.