Laboratory Anaerobic Digesters Research Articles

ANAEROBIC CO-DIGESTION OF DIFFERENT MIXTURES OF ORGANIC WASTES – OUR EXPERIENCE

Anaerobic digestion is a biotechnological method of biogas generation from organic wastes. Anaerobic co-digestion can be considered as the instantaneous anaerobic digestion of two or more substrate and co-substrate mixtures. Anaerobic co-digestion is a pragmatic method to resolve the difficulties related to substrate properties and system optimization in single-substrate anaerobic digestion. During the last two decades our multidisciplinary team performed a lot of experiments of anaerobic co-digestion of different organic wastes activated sludge, cattle manure, swine manure, milk whey, wasted fruits and vegetables etc. Different ratios of mixtures of these organic wastes, in binary and triple mixtures, have been investigated in view to maximize the obtained energy (methane) production. The time for reaching of the process steady state in laboratory anaerobic digesters have been determined to be ten days’ period. Results obtained have shown that some binary mixtures are more perspective in regards to biogas production optimization. It has been found that the addition of 3rd substrate to some binary mixtures could lead to decrease of bioprocess effectiveness.

The Efficiency of Industrial and Laboratory Anaerobic Digesters of Organic Substrates: The Use of the Biochemical Methane Potential Correction Coefficient

This study is an elaboration on the conference article written by the same authors, which presented the results of laboratory tests on the biogas efficiency of the following substrates: maize silage (MS), pig manure (PM), potato waste (PW), and sugar beet pulp (SB). This article presents methane yields from the same substrates, but also on a technical scale. Apart from that, it presents an original methodology of defining the Biochemical Methane Potential Correction Coefficient (BMPCC) based on the calculation of biomass conversion on an industrial scale and on a laboratory scale. The BMPCC was introduced as a tool to enable uncomplicated verification of the operation of a biogas plant to increase its efficiency and prevent undesirable losses. The estimated BMPCC values showed that the volume of methane produced in the laboratory was overestimated in comparison to the amount of methane obtained under technical conditions. There were differences observed for each substrate. They ranged from 4.7% to 17.19% for MS, from 1.14% to 23.58% for PM, from 9.5% to 13.69% for PW, and from 9.06% to 14.31% for SB. The BMPCC enables estimation of biomass under fermentation on an industrial scale, as compared with laboratory conditions.

Biodiversity-function relationships in methanogenic communities.

Methanogenic communities play a crucial role in carbon cycling and biotechnology (anaerobic digestion), but our understanding of how their diversity, or composition in general, determines the rate of methane production is very limited. Studies to date have been correlational because of the difficulty in cultivating their constituent species in pure culture. Here, we investigate the causal link between methanogenesis and diversity in laboratory anaerobic digesters by experimentally manipulating the diversity of cultures by dilution and subsequent equilibration of biomass. This process necessarily leads to the loss of the rarer species from communities. We find a positive relationship between methane production and the number of taxa, with little evidence of functional saturation, suggesting that rare species play an important role in methane‐producing communities. No correlations were found between the initial composition and methane production across natural communities, but a positive relationship between species richness and methane production emerged following ecological selection imposed by the laboratory conditions. Our data suggest methanogenic communities show little functional redundancy, and hence, any loss of diversity—both natural and resulting from changes in propagation conditions during anaerobic digestion—is likely to reduce methane production.

Use of laboratory anaerobic digesters to simulate the increase of treatment rate in full-scale high nitrogen content sewage sludge and co-digestion biogas plants

The aim of this study was to assess the effect of increasing feedstock treatment rate on the performance of full-scale anaerobic digestion using laboratory-scale reactors with digestate and feedstock from full-scale digesters. The studied nitrogen-containing feedstocks were i) a mixture of industrial by-products and pig slurry, and ii) municipal sewage sludge, which digestion was studied at 41 and 52°C, respectively. This study showed the successful reduction of hydraulic retention times from 25 and 20days to around 15days, which increased organic loading rates from 2 to 3.5kg volatile solids (VS)/m3d and 4 to 6kgVS/m3d. As a result, the optimum retention time in terms of methane production and VS removal was 10–15% lower than the initial in the full-scale digesters. Accumulation of acids during start-up of the co-digestion reactor was suggested to be connected to the high ammonium nitrogen concentration and intermediate temperature of 41°C.

Bioaugmentation of biogas production by a hydrogen-producing bacterium

The rate-limiting nature of the hydrogen concentration prevailing in the anaerobic digester has been recognized, but the associated alterations in the microbial community are unknown. In response to the addition of Enterobacter cloacae cells in laboratory anaerobic digesters, the level of biogas production was augmented. Terminal restriction fragment length polymorphism (T-RFLP) and real-time polymerase chain reaction (Real-Time PCR) were used to study the survival of mesophilic hydrogen-producing bacteria and the effects of their presence on the composition of the other members of the bacterial community. E. cloacae proved to maintain a stable cell number and to influence the microbial composition of the system. Bioaugmentation by a single strain added to the natural biogas-producing microbial community was demonstrated. The community underwent pronounced changes as a result of the relatively slight initial shift in the microbiological system, responding sensitively to the alterations in local hydrogen concentration.

Counteracting ammonia inhibition in anaerobic digestion by removal with a hollow fiber membrane contactor

The aim of the current study was to investigate the feasibility of membrane contactors for continuous ammonia (NH3–N) removal in an anaerobic digestion process and to counteract ammonia inhibition. Two laboratory anaerobic digesters were fed slaughterhouse wastes with ammonium (NH4+) concentrations ranging from 6 to 7.4 g/L. One reactor was used as reference reactor without any ammonia removal. In the second reactor, a hollow fiber membrane contactor module was used for continuous ammonia removal. The hollow fiber membranes were directly submerged into the digestate of the anaerobic reactor. Sulfuric acid was circulated in the lumen as an adsorbent solution. Using this set up, the NH4+–N concentration in the membrane reactor was significantly reduced. Moreover the extraction of ammonia lowered the pH by 0.2 units. In combination that led to a lowering of the free NH3–N concentration by about 70%. Ammonia inhibition in the reference reactor was observed when the concentration exceeded 6 g/L NH4+–N or 1–1.2 g/L NH3–N. In contrast, in the membrane reactor the volatile fatty acid concentration, an indicator for process stability, was much lower and a higher gas yield and better degradation was observed. The chosen approach offers an appealing technology to remove ammonia directly from media having high concentrations of solids and it can help to improve process efficiency in anaerobic digestion of ammonia rich substrates.

Anaerobic Co-Digestion of table olive debittering & washing Effluent, cattle manure and pig manure in batch and high volume laboratory anaerobic digesters: Effect of temperature

The prospective of table olive debittering & washing Effluent (DWE) as feed stock wastewater for anaerobic digestion (AD) systems was investigated in batch and continuous systems together with cattle and pig manures. While DWE considered unsuitable for biological treatment methods due to its unbalanced nature, the co-digestion of the wastewaters resulted in a 50% increase in the methane production/gram volatile solidsadded (CH4/gVSadded), accompanied by 30% phenol reduction and 80% total organic carbon removal (TOC). pH increase during the co-digestion period was not identified as an inhibitory factor and all reactors were able to withstand this operational condition change. Moreover, no volatile fatty acid (VFA) accumulation was observed, indicating that the reactors were not operating under stress-overloading state. Under thermophilic conditions a 7% increase on the TOC removal efficiency was achieved when compared to the mesophilic systems while, under mesophilic conditions phenolic compounds reduction was 10% higher compared to the thermophilic systems.

Enhancement of Sludge Reduction and Methane Production Rates Using Different Pretreatment Methods Applied Prior to Small Scale Laboratory Anaerobic Digesters

Enhancement of Sludge Reduction and Methane Production Rates Using Different Pretreatment Methods Applied Prior to Small Scale Laboratory Anaerobic Digesters

Enhancement of Sludge Reduction and Methane Production Rates Using Different Pretreatment Methods Applied Prior to Small Scale Laboratory Anaerobic Digesters

Enhancement of Sludge Reduction and Methane Production Rates Using Different Pretreatment Methods Applied Prior to Small Scale Laboratory Anaerobic DigestersRapidly increasing sludge quantities and limitations on reliable disposal methods compelled the researchers to look for methods to minimize the generation rates. Sludge pretreatment prior to anaerobic digestion emerged as a potential application. Pretreatment using physical, chemical, biological, mechanical or combined methods when applied prior to anaerobic digestion, not only increases the...Author(s)Gozde T. ZorbaIlgin AtalarO. Guven ApulF. Dilek SaninSourceProceedings of the Water Environment FederationSubjectSession 10: Anaerobic Digestion Pretreatment for Enhanced PerformanceDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:4L.675;1-DOI10.2175/193864710802767849Volume / Issue2010 / 4Content sourceResiduals and Biosolids ConferenceFirst / last page(s)675 - 686Copyright2010Word count365Subject keywordsAcid treatmentalkali treatmentanaerobic digestionmethanemicrowavesludge pretreatmentsludge reductionultrasound

Methodology for determination of anaerobic digestion kinetics using a bench top digester

This paper presents a methodology for determining the microbial growth kinetics of an ideal anaerobic process in a non-ideal laboratory anaerobic digester (Armfield). Some laboratory experiments were performed, to confirm the proposed methodology. Having the same zero biomass concentration, some process parameters were changed and their influence on substrate outlet concentration was monitored. The specific growth rate of the biomass, the saturation constant of the substrate, and the yield coefficient were calculated, on the basis of the measured values. These parameters enabled us to perform a dynamic simulation of an anaerobic process in ideal continuously-stirred tank reactors (CSTR). The results represented the mass concentration profiles for substrate and biomass, from which the time required for reaching the steady state (60 d), where the operation is optimal, could be determined. The laboratory anaerobic digester provided operational process data, which are applicable for wastewater treatment plant design purposes.

Ultrasonic cell disruption of stabilised sludge with subsequent anaerobic digestion

The world-wide increasing environmental awareness and its subsequent regulations have led to the application of improved technologies in wastewater purification plants. This has resulted in higher wastewater and sludge productions. Sludge is the by-product of such plants and it is not only rich in organic carbon and pathogens but also in heavy metals and other environmental pollutants. In Europe, agricultural application of dried sludge (bio-solids) is confronted with negative reactions from the citizens, governmental organisations, farmers and the food industry. Ultrasonic disruption of sludge is a popular mechanical disruption process in sludge treatment. During ultrasonic treatment, high frequency acoustic signals are used to initiate the cavitation process. The applied ultrasonic field leads to a breakdown of cohesive forces of the liquid molecules resulting in the generation of cavitation bubbles. A shock wave is released by the collapse of the cavitation bubbles and propagates in the surrounding medium forming jet streams that cause the disruption of cells in sludge. Disruption of sludge cells enables the release of light organic substances into the sludge water thereby exposing them for further anaerobic digestion. This paper presents results on the disruption of conventionally stabilised sludge through the application of the ultrasonic field. In order to reduce the specific energy input (i.e. ratio of the consumed energy during ultrasonic disruption to the input sludge mass) and improve biogas production, the total solids content of the stabilised sludge was increased before disruption. The anaerobic digestion of sludge samples was carried out in a set of specially constructed laboratory anaerobic digesters. Results showed that subsequent anaerobic digestion of the ultrasonically disrupted sludge could improve biogas production with reduced sludge quantity that is vital to the economic consideration of the wastewater treatment plants. This process encourages the exploitation of valuable materials and energy from stabilised sewage sludge just before its final disposal. The negative effects of mixing disrupted sludge with its separated sludge water are also shown in this paper. This expresses the microbiological instability of the anaerobic process caused by the mixing process.

Laboratory investigation of supported permeable organic covers for the management of odour emissions from anaerobic piggery waste ponds

Australian research has linked much of the odour arising from intensive livestock operations to pond treatment systems. A reduction in emissions from treatment ponds would therefore generally reduce odour emissions from intensive livestock operations. Published data indicates that the application of straw and other biological materials to effluent pond surfaces as a continuous cover reduces odour emissions. The effectiveness of these covers has not, however, been researched under controlled conditions. Using locally available materials, the efficacy of supported covers has been investigated using a series of laboratory anaerobic digesters treating typical piggery effluent. Research to date has focused on: identifying effective cover and cover support materials; quantifying odour reduction; identifying the impact use these covers may have on greenhouse gas emissions; devising practical and effective methods for constructing these covers. Results have confirmed that a variety of cover materials are effective in reducing pond odour emissions. Supporting the pond cover appears to extend the cover life expectancy. While greenhouse gas emissions appear to vary according to cover type, the overall significance of these emissions is not yet clear. The impact of permeable pond covers on overall pond performance requires additional research.

Dissolved hydrogen concentration as an on-line control parameter for the automated operation and optimization of anaerobic digesters

The use of dissolved hydrogen as an early warning signal of digester failure and a control parameter to operate anaerobic digesters was investigated. A sensitive, on-line method was developed for measuring trace levels of dissolved hydrogen in a semi-permeable membrane, situated within the biomass of a 1 L laboratory anaerobic digester, using trace reduction gas analysis. At normal operating conditions, the dissolved hydrogen partial pressure (2 to 8 Pa) was found to be linearly correlated with the loading rate of the digester, and was a sensitive indicator of the effect of shockloads as well as gradual overloading. An increase in hydrogen partial pressure above a critical concentration of 6.5-7 Pa indicated the initial stage of digester overloading (i.e., volatile fatty acids accumulation). A H(2)-based computer control system, using a critical hydrogen partial pressure of 6.5 Pa as the setpoint, was found to be effective for the safe operation of a laboratory digester close to its maximum sustainable loading rate. The existence of a relationship between hydrogen level and organic loading rate was also confirmed on a 600 m(3) industrial digester, with digester overloading occurring at hydrogen concentrations above 7 Pa. The results suggest that the dissolved hydrogen concentration is capable of being a sensitive on-line parameter for the automated management of anaerobic digesters near their maximum sustainable loading capacity. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 626-634, 1997.

Low-temperature digestion of dairy and swine manure

Laboratory anaerobic digesters were fed dairy and swine manure at the rates of 0.1 and 0.2 kg volatile solids (VS)/ m 3-day over the temperature range of 10–23°C. The digesters were operated successfully with little indication of instability. Methane (CH 4) yield, (B, m 3 CH 4/kg VS added) was determined to typically decrease linearly as temperature (T, °C) was decreased: Dairy at 0.1 kg VS/m 3-day B=0.1153+0.0053T Dairy at 0.2 kg VS/m 3-day B=0.0820+0.0063T Swine at 0.1 kg VS/m 3-day B=0.2011+0.0053T Swine at 0.2 kg VS/m 3-day B=0.3177+0.0044T Some increased performance was suggested for the lower loading rates compared with higher loading rates.

Bioaugmentation of anaerobic digestion with a biocatalytic addition: The bacterial nature of the biocatalytic addition

Biocatalytic additions and bioenzymes are frequently marketed to be able to improve the performance of wastewater process units. There have, however, been conflicting reports on the usefulness of such biocatalytic additions. The bacterial nature of a particular commercial biocatalyst is studied here. Pure culture techniques were used to isolate the bacteria growing on selected culture media, and results were compared with the bacteria recovered in a laboratory anaerobic digester. The limited range of bacteria identified comprised either obligate aerobes or facultative anaerobes, and no methanogens were detected. Considering that there was no significant difference in the bacterial flora in reactors with, as well as without the biocatalytic addition, there was therefore insufficient evidence to support the use of the biocatalyst in the anaerobic digestion process.

A laboratory study of struvite precipitation after anaerobic digestion of piggery wastes

A dilute (0·3% TS) but relatively strong (COD 10 000 mg litre −1) piggery wastewater was used as feed in 1·6-litre laboratory anaerobic digesters. During batch digestion (56 days), NH 3-N increased from 500 to 800 mg litre −1 and PO 4-P from 21 to 30 mg litre −1 while Mg concentrations decreased from 32 to 20 mg litre −1. A continuously fed digester (mean residence time of 64 days) produced similar increases in NH 3-N concentrations and reductions in concentrations of PO 4-P (22 to 10 mg litre −1) and Mg from 32 to 20 mg litre −1. X-ray diffraction of the digester sludge indicated that langbeinite (K 2Mg(SO 4) 3) was precipitated whilst it appeared that very fine crystals of Ca, Mg and PO 4 compounds remained in suspension. The addition of MgSO 4 to the batch supernate raised to a pH of 9 led to a reduction in PO 4-P concentrations from 33 to 7 mg litre −1 and the supernate from the continuous digester at a pH of 9 from 10 to 0·1 mg litre −1. The precipitate formed by this reaction was comprised of struvite (MgNH 4PO 4.6H 2O), apthitatite (K 3Na(SO 4) 2) and thermarite (Na 3SO 4). The reduction of PO 4-P concentrations to less than 1 mg litre −1, a significant water quality criterion in the management of eutrophication, is of importance. The production of struvite as a valuable fertilizer may offset much of the cost of this form of wastewater treatment.

Determination of bicarbonate and total volatile acid concentration in anaerobic digesters using a simple titration

ABSTRACT: A simple, alkalimetric method is described that can be used to determine bicarbonate and total volatile fatty acid concentrations in anaerobic digesters by a two‐stage sequential titration. The new method was evaluated by standard solutions of volatile fatty acids and bicarbonate over a pH 5.5 to 7.65 range. It was also used to determine the total volatile fatty acid and bicarbonate concentrations in effluent samples from five laboratory anaerobic digesters treating different types of waste. The average recovery of volatile fatty acids and bicarbonate by the new method from standard solutions was found to be 96%. The total volatile fatty acid concentration measured by the new method from the digester ceffluent samples coincided well with those measured by a chromatographer.

A new device for measurement and control of gas production by bench scale anaerobic digesters

On the basis of an analysis, in terms of desirable characteristics and main sources of error, of existing apparatus for measuring biogas production by laboratory anaerobic digesters, we have developed a new device that is precise, inexpensive, easily constructed and capable of functioning autonomously for long periods. A slightly costlier version suitable for use in automatic control systems is also described.

Characterization of polysaccharidase activity optima in the anaerobic digestion of municipal solid waste

Cellulolytic enzymes from a laboratory anaerobic digester fed municipal solid waste were examined with respect to pH and temperature. The pH optimum was pH 6.6, considerably lower than the pH range in which digesters are normally operated (pH 7.2–7.6). The optimum temperature was between 50 and 60°C, rather than the 35–37°C range in which most digesters are controlled.

Production of trace levels of carbon monoxide during methanogenesis on acetate and methanol

Production of trace levels of carbon monoxide was consistently observed in the off-gas of a laboratory anaerobic digester fed Waste Activated Sludge. Inocula from this digester was enriched for acetate and methanol utilizing methanogenic populations. These enriched inocula were then monitored in batch assays for carbon monoxide and hydrogen production. Results demonstrated that carbon monoxide is produced during methanogenesis on both substrates. Subsequent utilization of CO was observed to occur after methane production was essentially complete for the assays conducted with methanol. Carbon monoxide evolution during methanogenesis on acetate displayed a markedly different trend from that observed from methanol.