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Abstract: Anaerobic digestion (AD) of complex substrates is a multi-step process, which is kinetically controlled by an individual rate-limiting step. A methodology for determining the rate-limiting step during AD of complex substrates was developed by supplementation of metabolic intermediates from each digestion step with dairy manure as an emblematic complex substrate. This method elucidated that hydrolysis of dairy manure was the rate-limiting step when normal anaerobic sludge was used as inoculum. Furthermore, the concept and effect of microbial community ratio was introduced by manipulating two different inocula, i.e. normal anaerobic sludge and heated anaerobic sludge, so that varying ratios (r) of hydrolytic and methanogenic bacteria could be studied. Results revealed that the rate-limiting step changed with the variation of r. For dairy manure, results indicated a critical ratio r ∗ =24 between hydrolytic bacteria and methanogens, whereby as r decreased or exceeded from this value, hydrolysis or methanogenesis limited the AD process, respectively. [Copyright &y& Elsevier]

A new anaerobic digester design for the treatment of diluted (<2% solids) flush dairy manure was evaluated. The new design was developed as an economic alternative for enhancing the performance of anaerobic lagoon systems in cold weather areas. The digester employed used automobile tires as fixed-bed media to improve bacterial retention. The digester was heated by steam injection and built underground to enhance insulation. The tires were sorted in a unique pattern for improving mixing and uniform temperature distribution. The system was tested on a pilot-scale. The treatment mechanism was explored by mathematical modeling. The observed treatment efficiency of the new design was comparable to that of conventional digesters operating at higher total solids concentrations (>4%). With a hydraulic retention time (HRT) of 17 days, the measured removal rates were 30–50% and 40–60% of TVS and COD, respectively. The new digester maintained longer solids retention time (SRT) as estimated using the model, supported by the observed thick biofilm formation and resistance to hydraulic overload. The model was used to analyze different operation scenarios varying both the organic and hydraulic loads. [Copyright &y& Elsevier]

The inhibition effect of four antibiotics, i.e. ampicillin (AMP), tylosin (TYL), florfenicol (FLO) and sulfamethazine (SMT), was investigated in dairy manure digesters for both single dosing and semi-continuous dosing operations over a period of 40 days. High throughput 16S rRNA sequence analysis revealed that dosing mode did have significant impact on microbial community, i.e. antibiotics had a notable effect on bacteria in single dosing digesters, while archaea were the major population affected in the semi-continuous dosing operations. FLO shows the most severe inhibition on biogas production and remarkably effected bacterial communities, which led to a complete upset of the whole community. Although the effect of SMT on biogas production was marginal, methanogens populations were notably shifted. A four-stage inhibition process on microbial community was proposed based on the ratio of the affected bacteria to archaea to shed new light on microbial population dynamics during anaerobic digestion. Moreover, we found that the semi-continuous operation mode of antibiotics is more efficient in terms of microbial community changes, which may guide the formulation of veterinary drug doses and cycle intervals. [Display omitted] • Antibiotics dosing mode had significant different impact on microbial community. • Antibiotics affect bacteria in single dosing reactor but archaea in semi-continuous one. • Four-stage community change process proposed based on affected bacteria to archaea ratio. [ABSTRACT FROM AUTHOR]

The major concern of recycling anaerobic digestion (AD) effluent in the digester centers on accumulation of total ammonia nitrogen (TAN) and salinity, both of which can potentially inhibit methane production. In the current study, 30%, 50%, and 80% of separated-liquid AD effluent, were recycled in a series of batch AD experiments. The inhibitions to specific methane potential (SMP) caused by TAN and salinity were evaluated. Recycling up to 80% of un-treated effluent resulted in the best SMP averaging 0.265 ± 0.005 m 3 [CH 4 ] Kg −1 [volatile solids], which averaged 10% more compared to recycling 80% treated effluent and 5% more compared to no recycling (the control). After acclimation, up to 6.39 g N L −1 increase in TAN resulted in SMP averaging 0.112 ± 0.002 m 3 [CH 4 ] Kg −1 [volatile solids] and up to 12 parts per thousand increase in salinity resulted in SMP averaging 0.163 ± 0.005 m 3 [CH 4 ] Kg −1 [volatile solids]. A mass balance for a hypothetical 5000 cows dairy farm showed effluent recycle of up to 66% for maintaining 8% solids in anaerobic digester. Moreover, in the proposed system, the effluent going off-farm was on w/w basis 64% less water, 66% less solids, and 52% less nitrogen compared to the effluent produced with no recycle facility. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a new strategy, improving biomass retention with fiber material present within the dairy manure as biofilm carriers, was evaluated for treating flushed dairy manure in a psychrophilic anaerobic sequencing batch reactor (ASBR). A kinetic study was carried out for process control and design by comparing four microbial growth kinetic models, i.e. first order, Grau, Monod and Chen and Hashimoto models. A volumetric methane production rate of 0.24L/L/d of and a specific methane productivity of 0.19L/gVSloaded were achieved at 6days HRT. It was proved that an ASBR using manure fiber as support media not only improved methane production but also reduced the necessary HRT and temperature to achieve a similar treating efficiency compared with current technologies. The kinetic model can be used for design and optimization of the process. [Copyright &y& Elsevier]

Fumaric acid is widely used as a food additive for flavor and preservation. Rhizopus oryzae ATCC 20344 is a fungus known for good fumaric acid production. It also has been reported that the fungal biomass has high chitin content. This study investigated the possibility of producing both fumaric acid and chitin via R. oryzae fermentation of dairy manure. Co-production of valuable bio-based chemicals such as fumaric acid and chitin could make the utilization of manure more efficient and more profitable. A three step fermentation process was developed which effectively utilized the nitrogen as well as the carbohydrate sources within the manure. These steps were: the culturing of pellet seed; biomass cultivation on liquid manure to produce both biomass and chitin; and fumaric acid production on the hydrolysate from the manure fiber. Under the identified optimal conditions, the fermentation system had a fumaric acid yield of 31%, and a biomass concentration of 11.5g/L that contained 0.21gchitin/gbiomass. [Copyright &y& Elsevier]

Abstract The dynamics of microbial communities during anaerobic digestion at different states of acclimation and inhibitions is key to diagnosing ailments of this process. Previous studies focused primarily on concentrations thresholds for inhibition and adaptation. This study investigated the dynamics of methane (CH 4) producing communities subjected to ammonia and salinity stresses during batch anaerobic digestion, of dairy wastewater, in both acclimated and unacclimated conditions. Experimental data was fitted into the 'Modified Gompertz Model' and resulting lag phase values related to stress conditions. R2-values ranged between 0.95 and 1.00 suggesting a nearly perfect fit of the model to the observed CH 4 production. Irrespective of acclimation conditions, digesters under ammonia stresses produced less CH 4 compared to those subjected to salinity stresses. Salinity-acclimated digesters performed similar to salinity-free digesters below 12 g L−1 salinity level. Petrimonas and Clostridium XI were the most dominant (50–61%) bacterial genera in salinity-acclimated digesters, whereas Petrimonas, Clostridium XI , Alkaliflexus, Sedimentibacter, and Clostridium III were the most abundant (69–82%) bacterial genera in salinity-unacclimated digesters. In ammonia-acclimated digesters, Petrimonas , Clostridium XI , and Alkaliflexus were the most dominant (55–68%) genera. Petrimonas, Clostridium XI , Alkaliflexus, Sedimentibacter, Clostridium III , Clostridium XIVa , were the most abundant (74–87%) bacterial genera in TAN-unacclimated digesters. Methanosarcina , Methanobrevibacter and Methanobacterium were most abundant archaea in both salinity (71–99%) and ammonia (87–98%) stressed digesters. The principal component analysis demonstrated bacteria clustering in the acclimated and the unacclimated reactors. No such clustering of archaea was evident in either acclimated or unacclimated reactors. Highlights • Ammonia resulted in higher inhibition to CH 4 yield than salinity. • The Gompertz model adequately (95–100%) predicted inhibited CH 4 yields. • Methanosarcina tolerate higher inhibitior levels than other archaea. • Acclimation improved inhibition tolerance and CH 4 yield. [ABSTRACT FROM AUTHOR]

One of the consequences of the increase of large dairy concentrated feeding operations (CAFOs) is the abundance of dairy manure that needs to be disposed of or used in some way. CAFOs can become bio-refineries, harnessing the manure for heat, power, fuel, chemicals, fertilizers, fiber, wood composites, and biochar for production of multiple value-added co-products. The objective of this paper is to review options for using dairy manure fiber and its corresponding anaerobically digested (AD) fiber. Bedding for cows remains a common choice for employing the separated AD fiber. However, research has shown that AD fiber has potential for using it as a component of growth substrates used in container plant production systems, for producing composite materials, or as a feedstock for both chemical and thermochemical operations. Potential uses of AD fiber such as composite materials and liquid fuels are proposed based on experiences employing the manure and its fiber (both without a previous AD step and after AD). Thermochemical processing (e.g., liquefaction and pyrolysis) of AD fiber for fuels and chemicals has been conducted at laboratory level and still needs further study at larger scale. Gasification of AD fiber is a promising option since there is potential for integration of current methane production with methane produced from thermal gasification. [ABSTRACT FROM AUTHOR]

Confined animal feeding operations (CAFOs) contribute to greenhouse gas emission, but the magnitude of these emissions as a function of operation size, infrastructure, and manure management are difficult to assess. Modeling is a viable option to estimate gaseous emission and nutrient flows from CAFOs. These models use a decomposition rate constant for carbon mineralization. However, this constant is usually determined assuming a homogenous mix of manure, ignoring the effects of emerging manure treatments. The aim of this study was to measure and compare the decomposition rate constants of dairy manure in single and three-pool decomposition models, and to develop an empirical model based on chemical composition of manure for prediction of a decomposition rate constant. Decomposition rate constants of manure before and after an anaerobic digester (AD), following coarse fiber separation, and fine solids removal were determined under anaerobic conditions for single and three-pool decomposition models. The decomposition rates of treated manure effluents differed significantly from untreated manure for both single and three-pool decomposition models. In the single-pool decomposition model, AD effluent containing only suspended solids had a relatively high decomposition rate of 0.060 d −1 , while liquid with coarse fiber and fine solids removed had the lowest rate of 0.013 d −1 . In the three-pool decomposition model, fast and slow decomposition rate constants (0.25 d −1 and 0.016 d −1 respectively) of untreated AD influent were also significantly different from treated manure fractions. A regression model to predict the decomposition rate of treated dairy manure fitted well (R 2 = 0.83) to observed data. [ABSTRACT FROM AUTHOR]

A direct aeration strategy was developed for ammonia recovery without alkali addition. The main chemical buffer system of digested effluent is made up of high concentration of acidic species, which lead to a hypothesis that elevation of pH for ammonia release could be achieved by removing supersaturated CO 2 , dissolved carbonate, and bicarbonate solely. The concept was tested in lab scale reactors with digested dairy manure focusing on temperature, bubble size, liquid depth and airflow rate. It has demonstrated that simple air stripping without alkali chemical input is an effective way to elevate pH of the digested effluent due to intriguing chemical shifts strongly related to the high levels of carbon dioxide, bicarbonates and carbonates present in digested effluent. These chemical shifts, ultimately release carbon dioxide and raise the pH of the effluent to levels near 10, which with combined elevated operating temperatures from waste engine heat, can lead to 70–90% shift from ionic to free, gaseous form of ammonia and subsequent recovery of ammonia through acid contact. The chemical relationships and equilibrium shifts associated with the aeration process and its subsequent release of gases were further investigated by chemical equilibrium model. [ABSTRACT FROM AUTHOR]

Abstract: The objectives of this study were to statistically study the effects of reaction conditions of temperature, acid concentration, and reaction time on manure components of cellulose, hemicellulose, lignin, and nitrogen during dilute acid treatment of dairy manure; and to further optimize the accumulation of cellulose for later enzymatic conversion to glucose. A 23 full factorial design was adopted to investigate the effects of the reaction conditions on each individual component and later followed by a 3-factor central composite design which was used to obtain the optimal conditions for cellulose accumulation. The results indicated that acid was the most important factor for changes of all the components. The results also showed that two other individual factors, reaction time and temperature, as well as the interactions among all three factors had significant influences on the changes. In addition, the optimal conditions for cellulose accumulation were 2.8h reaction time, 140°C reaction temperature, and 1.0% acid concentration. Under these conditions cellulose content reached 31.0% while hemicellulose, lignin and nitrogen content were 3.2%, 20.8% and 2.4%, respectively. [Copyright &y& Elsevier]