Bioaugmenting anaerobic digestion of biosolids with selected strains of Bacillus, Pseudomonas, and Actinomycetes species for increased methanogenesis and odor control

Scientific characterization methods for better utilization of cattle dung and urine: a concise review

Cattle are usually raised for food, manure, leather, therapeutic, and draught purposes. Biowastes from cattle, such as dung and urine, harbor a diverse group of crucial compounds, metabolites/chemicals, and microorganisms that may benefit humans for agriculture, nutrition, therapeutics, industrial, and other utility products. Several bioactive compounds have been identified in cattle dung and urine, which possess unique properties and may vary based on agro-climatic zones and feeding practices. Therefore, cattle dung and urine have great significance, and a balanced nutritional diet may be a key to improved quality of these products/by-products. This review primarily focuses on the scientific aspects of biochemical and microbial characterization of cattle biowastes. Various methods including genomics for analyzing cattle dung and gas chromatography-mass spectroscopy for cattle urine have been reviewed. The presented information might open doors for the further characterization of cattle resources for heterogeneous applications in the production of utility items and addressing research gaps. Methods for cattle's dung and urine characterization.

Strategies for energy conversion from sludge to methane through pretreatment coupled anaerobic digestion: Potential energy loss or gain

Anaerobic digestion (AD) of wasted activated sludge from wastewater plants is recognized as an effective method to reclaim energy in the form of methane. AD performance has been enhanced by coupling various pretreatments that impact energy conversion from sludge. This paper mainly reviewed the development of pretreatments based on different technologies reported in recent years and evaluated their energy benefit. Significant increases in methane yield are generally obtained in AD with pretreatments demanding energy input, including thermal- and ultrasound-based methods. However, these energy-intense pretreatments usually gained negative energy benefit that the increase in methane yield consumed extra energy input. The unbalanced relationship counts against the goal of energy reclamation from sludge. Combined pretreatment consisting of multiple technologies normally outcompetes the single pretreatment, and the combination of energy-intense methods and chemicals potentially reduces energy input and simultaneously ensure high methane yield. For determining whether the energy reclamation from sludge via AD contribute to mitigating global warming, integrating greenhouse gas emission into the evaluation system of pretreated AD is further warranted.

Carbon cloth amendment for boosting high-solids anaerobic digestion with percolate recirculation: Spatial patterns of microbial communities

The addition of conductive materials in anaerobic digestion (AD) is a promising method for boosting biomethane recovery from organic waste. However, conductive additives have rarely been investigated for the high-solids anaerobic digestion (HSAD). Here, the impact of adding carbon cloth in the solid phase of an HSAD system with percolate recirculation was investigated. Furthermore, spatial patterns of microbial communities in suspended biomass, percolate, and carbon cloth attached biofilm were assessed. Carbon cloth increased biomethane yield from source-separated organics (SSO) by 20% more than the unamended control by shortening the lag phase (by 15%) and marginally improving the methanogenesis rate constant (by ∼8%) under a batch operation for 50 days. Microbial community analysis demonstrated higher relative abundances of the archaeal population in the carbon cloth amended reactor than in unamended control (12%-21% vs. 5%-15%). Compared to percolate and suspension, carbon cloth attached microbial community showed higher enrichment of known electroactive Pseudomonas species along with Methanosarcina and Methanobacterium species, indicating the possibility of DIET-based syntrophy among these species.

Methods of pretreatment and their impacts on anaerobic codigestion of multifeedstocks: A review

Anaerobic codigestion (AnCoD) has attracted attention owing to its advantages over conventional anaerobic digestion, and attempts are still going on to develop methods for improving the efficiency of this technology. Mostly, addition of cosubstrates without applying a proper pretreatment cannot adequately enhance the performance of the digestion. However, there is a lack of a comprehensive study on different pretreatment methods specific to the wide range of cosubstrates. This review aimed to (i) categorize pretreatment techniques that have been developed for improving AnCoD, (ii) present the results of the studies on the effect of pretreatment on improving AnCoD, and (iii) provide a comparison between pretreatment methods and their application for different types of cosubstrates. The findings primarily validated the influence of pretreatment to enhance the process by increasing biodegradability, improved hydrolysis, reduced hydraulic retention time (HRT), and improved methane production. The five main categories of pretreatment employed in codigestion included the following: mechanical, thermal, chemical, biological, and hybrid pretreatment. Among them, mechanical and biological pretreatment have the most and least application in codigestion, respectively. Greater efforts are required on the application of biological pretreatment and cost-benefit analysis of different pretreatment options on the variety of the cosubstrates. PRACTITIONER POINTS: Pretreatment can significantly enhance biomethane production in anaerobic digestion Anaerobic codigestion along with pretreatment can further enhance the conventional anaerobic digestion of single feedstock Mechanical and biological methods have been the most and least practiced pretreatment options Selection of applicable pretreatment option to enhance methane production is subject to the type of cosubstrates in the system There is a research gap in evaluating the application of biological pretreatment for various types of cosubstrates.

Effect of bioaugmentation on digestate metal concentrations in anaerobic digestion of sewage sludge

This study examined the influence of bioaugmentation on metal concentrations (aluminum, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel and zinc) in anaerobically digested sewage sludge. To improve the digestion efficiency, bioaugmentation with a mixture of wild-living Archaea and Bacteria (MAB) from Yellowstone National Park, USA, was used. The total concentration of all metals was higher in the digestate than in the feedstock. During anaerobic digestion, the percent increase in the concentration of most of metals was slightly higher in the bioaugmented runs than in the un-augmented runs, but these differences were not statistically significant. However, the percent increase in cadmium and cobalt concentration was significantly higher in the bioaugmented runs than in the un-augmented runs. At MAB doses of 9 and 13% v/v, cadmium concentration in the digestate was 211 and 308% higher than in the feedstock, respectively, and cobalt concentration was 138 and 165%, respectively. Bioaugmentation increased over 4 times the percentage of Pseudomonas sp. in the biomass that are able to efficiently accumulate metals by both extracellular adsorption and intracellular uptake. Biogas production was not affected by the increased metal concentrations. In conclusion, bioaugmentation increased the concentration of metals in dry sludge, which means that it could potentially have negative effects on the environment.

Effect of Bioaugmentation on Biogas Yields and Kinetics in Anaerobic Digestion of Sewage Sludge

Bioaugmentation with a mixture of microorganisms (Bacteria and Archaea) was applied to improve the anaerobic digestion of sewage sludge. The study was performed in reactors operating at a temperature of 35 °C in semi-flow mode. Three runs with different doses of bioaugmenting mixture were conducted. Bioaugmentation of sewage sludge improved fermentation and allowed satisfactory biogas/methane yields and a biodegradation efficiency of more than 46%, despite the decrease in hydraulic retention time (HRT) from 20 d to 16.7 d. Moreover, in terms of biogas production, the rate constant k increased from 0.071 h⁻¹ to 0.087 h⁻¹ as doses of the bioaugmenting mixture were increased, as compared to values of 0.066 h⁻¹ and 0.069 h⁻¹ obtained with sewage sludge alone. Next-generation sequencing revealed that Cytophaga sp. predominated among Bacteria in digesters and that the hydrogenotrophic methanogen Methanoculleus sp. was the most abundant genus among Archaea.

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.

Bioaugmentation and its application in wastewater treatment: A review

Bioaugmentation (the process of adding selected strains/mixed cultures to wastewater reactors to improve the catabolism of specific compounds, e.g. refractory organics, or overall COD) is a promising technique to solve practical problems in wastewater treatment plants, and enhance removal efficiency. The potential of this option can now be enhanced in order to take advantage of important advances in the fields of microbial ecology, molecular biology, immobilization techniques and advanced bioreactor design. Reports on bioaugmentation in WWT show the difficulties in evaluating the potential parameters involved, leading frequently to inconclusive outcomes. Many studies have been carried out on the basis of trial-and-error approaches, and it has been reported that reactors bioaugmented with pure cultures often fail to perform as well as the pure cultures under laboratory conditions. As an interesting technical challenge, the feasibility of bioaugmentation should ultimately be assessed by data from field implementation, and this review highlights several promising areas to explore in the future.

Outlining microbial community dynamics during temperature drop and subsequent recovery period in anaerobic co-digestion systems

To improve the stability of anaerobic reactors, more knowledge is required about how the different communities react against operating perturbations and which specific ones respond better. The objective of this work was to monitor the changes in microbial community structure of an anaerobic digester during a temperature drop by applying different complementary molecular techniques. Temperature decrease led to an increase of Bacteroidales order, Porphyromonadaceae family and Bacteroides genus and a decrease in Syntrophomonas and Clostridium genera. Once the temperature was restored, the reactor recovered the steady state performance without requiring any modification in operational conditions or in the microbiome. During the recovery period, Sedimentibacter genus and Porphyromonadaceae family played an important role in the degradation of the accumulated volatile fatty acids. The hydrogenotrophic methanogens appeared to be the keystone archaeal population at low temperatures as well as in the recovery period. This study stands out that the understanding of microbial community dynamics during temperature drop could be utilized to develop strategies for the mitigation of temperature change consequences and speed up the recovery of stable reactor performance.

Redundancy, resilience, and host specificity of the ruminal microbiota: implications for engineering improved ruminal fermentations

The ruminal microbial community is remarkably diverse, containing 100s of different bacterial and archaeal species, plus many species of fungi and protozoa. Molecular studies have identified a “core microbiome” dominated by phyla Firmicutes and Bacteroidetes, but also containing many other taxa. The rumen provides an ideal laboratory for studies on microbial ecology and the demonstration of ecological principles. In particular, the microbial community demonstrates both redundancy (overlap of function among multiple species) and resilience (resistance to, and capacity to recover from, perturbation). These twin properties provide remarkable stability that maintains digestive function for the host across a range of feeding and management conditions, but they also provide a challenge to engineering the rumen for improved function (e.g., improved fiber utilization or decreased methane production). Direct ruminal dosing or feeding of probiotic strains often fails to establish the added strains, due to intensive competition and amensalism from the indigenous residents that are well-adapted to the historical conditions within each rumen. Known exceptions include introduced strains that can fill otherwise unoccupied niches, as in the case of specialist bacteria that degrade phytotoxins such as mimosine or fluoroacetate. An additional complicating factor in manipulating the ruminal fermentation is the individuality or host specificity of the microbiota, in which individual animals contain a particular community whose species composition is capable of reconstituting itself, even following a near-total exchange of ruminal contents from another herd mate maintained on the same diet. Elucidation of the interactions between the microbial community and the individual host that establish and maintain this specificity may provide insights into why individual hosts vary in production metrics (e.g., feed efficiency or milk fat synthesis), and how to improve herd performance.

Wood ash amendment to biogas reactors as an alternative to landfilling? A preliminary study on changes in process chemistry and biology

Wood ash addition to biogas plants represents an alternative to commonly used landfilling by improving the reactor performance, raising the pH and alleviating potential limits of trace elements. This study is the first on the effects of wood ash on reactor conditions and microbial communities in cattle slurry-based biogas reactors. General process parameters [temperature, pH, electrical conductivity, ammonia, volatile fatty acids, carbon/nitrogen (C/N), total solids (TS), volatile solids, and gas quantity and quality] were monitored along with molecular analyses of methanogens by polymerase chain reaction- denaturing gradient gel electrophoresis and modern microarrays (archaea and bacteria). A prompt pH rise was observed, as was an increase in C/N ratio and volatile fatty acids. Biogas production was inhibited, but recovered to even higher production rates and methane concentration after single amendment. High sulphur levels in the wood ash generated hydrogen sulphide and potentially hampered methanogenesis. Methanosarcina was the most dominant methanogen in all reactors; however, diversity was higher in ash-amended reactors. Bacterial groups like Firmicutes, Proteobacteria and Acidobacteria were favoured, which could improve the hydrolytic efficiency of the reactors. We recommend constant monitoring of the chemical composition of the used wood ash and suggest that ash amendment is adequate if added to the substrate at a rate low enough to allow adaptation of the microbiota (e.g. 0.25 g g(-1) TS). It could further help to enrich digestate with important nutrients, for example phosphorus, calcium and magnesium, but further experiments are required for the evaluation of wood ash concentrations that are tolerable for anaerobic digestion.

Bioaugmentation of syntrophic acetate-oxidizing culture in biogas reactors exposed to increasing levels of ammonia

The importance of syntrophic acetate oxidation for process stability in methanogenic systems operating at high ammonia concentrations has previously been emphasized. In this study we investigated bioaugmentation of syntrophic acetate-oxidizing (SAO) cultures as a possible method for decreasing the adaptation period of biogas reactors operating at gradually increased ammonia concentrations (1.5 to 11 g NH(4)(+)-N/liter). Whole stillage and cattle manure were codigested semicontinuously for about 460 days in four mesophilic anaerobic laboratory-scale reactors, and a fixed volume of SAO culture was added daily to two of the reactors. Reactor performance was evaluated in terms of biogas productivity, methane content, pH, alkalinity, and volatile fatty acid (VFA) content. The decomposition pathway of acetate was analyzed by isotopic tracer experiments, and population dynamics were monitored by quantitative PCR analyses. A shift in dominance from aceticlastic methanogenesis to SAO occurred simultaneously in all reactors, indicating no influence by bioaugmentation on the prevailing pathway. Higher abundances of Clostridium ultunense and Tepidanaerobacter acetatoxydans were associated with bioaugmentation, but no influence on Syntrophaceticus schinkii or the methanogenic population was distinguished. Overloading or accumulation of VFA did not cause notable dynamic effects on the population. Instead, the ammonia concentration had a substantial impact on the abundance level of the microorganisms surveyed. The addition of SAO culture did not affect process performance or stability against ammonia inhibition, and all four reactors deteriorated at high ammonia concentrations. Consequently, these findings further demonstrate the strong influence of ammonia on the methane-producing consortia and on the representative methanization pathway in mesophilic biogas reactors.

Monitoring of bacterial communities during low temperature thermal treatment of activated sludge combining DNA phylochip and respirometry techniques

Sludge reduction is one of the major challenges in biological wastewater treatment. One approach is to increase the sludge degradation yield together with the biodegradation kinetics. Among the various sludge pretreatment strategies proposed, thermal pretreatment at around 65 °C was described as promising. The enhancement in the biodegradation activity due to the selection of thermophilic hydrolytic bacteria was proposed, but further experiments are needed to demonstrate the specific role of these bacteria. In this study, concentrated activated sludge grown at 20 °C was subjected to thermal treatment at 65 °C for different periods. The originality of the work relied on a polyphasic approach based on the correlation between kinetics (chemical oxygen demand, COD; mixed liquor suspended solids, MLSS), bacterial activity (respirometry) and bacterial community structure (phylochip monitoring) in order to characterize the mechanisms involved in the thermal reduction of sludge. The bacterial activity in the aeration basin decreased to a very low level when recycling sludge was treated at 65 °C from 13 to 60 h, but then, started to increase after 60 h. In parallel to these fluctuations in activity, a drastic shift occurred in the bacterial community structure with the selection of thermophilic bacteria (mainly related to genera Paenibacillus and Bacillus), which are known for their specific hydrolases.

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 < 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 H(2)-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.