Effect of organic loading and retention time on dairy manure fermentation

The investigations presented and discussed herein establish an enhanced understanding on volatile fatty acid (VFA) production as a function of dairy manure fermenter organic loading (OL) and retention time (RT), first through a factorial of 64 fermentation potential (FP) batch tests, followed by analysis of a continuously operated pilot-scale fermenter. The maximum observed net FP - 0.103 mg VFA produced (as COD) (mg VS applied)⁻¹ - occurred at an OL of 40.7 g VS L⁻¹ and at a RT of 6 days. The pilot-scale fermenter exhibited an average yield of 0.09 mg VFA (as COD) synthesized (mg VS applied)⁻¹, with average effluent total VFA concentrations of 6398 mg VFA (as COD) L⁻¹. The research demonstrates that FP tests are an effective method to optimize continuously operated dairy manure fermenters, and that dairy manure fermentation can yield large quantities of organic acids at short RTs and high OL rates.     

Dry anaerobic digestion of high solids content dairy manure at high organic loading rates in psychrophilic sequence batch reactor

Cow manure with bedding is renewable organic biomass available around the year on dairy farms. Developing efficient and cost-effective psychrophilic dry anaerobic digestion (PDAD) processes could contribute to solving farm-related environmental, energy, and manure management problems in cold-climate regions. This study was to increase the organic loading rate (OLR), fed to a novel psychrophilic (20 °C) dry anaerobic digestion of 27 % total solid dairy manure (cow feces and wheat straw) in sequence batch reactor (PDAD-SBR), by 133 to 160 %. The PDAD-SBR process operated at treatment cycle length of 21 days and OLR of 7.0 and 8.0 g total chemical oxygen demand (TCOD)?kg^?1 inoculum day^?1 (5.2?±?0.1 and 5.8?±?0.0 g volatile solids (VS)?kg^?1 inoculum day^?1) for four successive cycles (84 days) produced average specific methane yields (SMYs) of 147.1?±?17.2 and 143.2?±?11.7 normalized liters (NL)?CH₄?kg^?1 VS fed, respectively. PDAD of cow feces and wheat straw is possible with VS-based inoculum-to-substrate ratio of 1.45 at OLR of 8.0 g TCOD kg^?1 inoculum day^?1. Hydrolysis was the limiting step reaction. The VS removal averaged around 57.4?±?0.5 and 60.5?±?5.7 % at OLR 7.0 and 8.0 g TCOD kg^?1 inoculum day^?1, respectively.     

Methane production using whole and screened dairy manure in conventional and fixed-film reactors

The technical feasibility of adopting the fixed-film reactor concept for biogas production from screened dairy manure was investigated. The methane production capability of laboratory-scale 4-L anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at 35 degrees C was compared. Dairy manure filtrate with 4.4% total solids (TS) and 3.4% volatile solids (VS) (average value) was prepared from 1:1 manure-water slurry. The feed material was added intermittently at loading rates ranging from 2.34 to 25 and 2.25 to 785 g VS/L d, respectively, for the conventional and fixed-film reactors. Maximum methane production rate (L CH(4)/L d) for the conventional reactor was 0.63 L CH(4)/L d achieved at a 6-day hydraulic retention time (HRT). For the fixed-film reactor the maximum production rate was 3.53 L CH(4)/L d when operated at a loading rate of 262 g VS/L d (3 h HRT). The fixed-film reactor was capable of sustaining a loading of 785 g VS/L d (1 h HRT). The fixed-film reactor performed much better than the conventional reactors. These results indicate that a large reduction of required reactor volume is possible through application of a fixed-film concept combined with a liquid-solid separation pretreatment of dairy manure.     

Potentials of anaerobic treatment for catalytically oxidized olive mill wastewater (OMW)

The catalytically oxidized olive mill wastewater (OMW) was subjected to continuous anaerobic treatment using two treatment schemes. The 1st step in both schemes was an up-flow anaerobic sludge blanket (UASB) reactor (2 0 l). The 2nd step was either a hybrid UASB reactor or a classical one (1 0 l, each). The 1st stage was operated at constant hydraulic retention time (HRT) of 24 h. The organic loading rate (OLR) varied from 3.4 to 4.8 kgCOD/m³ d depending on the quality of the pretreated wastewater. The results obtained indicated that, the 1st step UASB reactor achieved a COD percentage removal value of 53.9%. Corresponding total BOD₅ and TSS removal were 51.5% and 68.3%, respectively.The results obtained indicated that the hybrid UASB reactor as a 2nd step produced better quality effluent as compared to the classical one. This could be attributed to the presence of the packing curtain sponge with active biomass in the sedimentation part of hybrid UASB reactor which minimizes suspended solids washout, consequently enhancement of the efficiency of the reactor.Available data showed that a two stage system consisting of a classical and a hybrid UASB reactor operated at a total HRT of 48 h and OLR of 2.0 kgCOD/m³ d provided promising results. Removal values of COD_total, BOD_5 total, TOC, VFA, oil and grease were 83%, 84%, 81%, 93% and 81%, respectively. Based on the available data, the use of a two stage anaerobic system consisting of a classical UASB reactor followed by a hybrid UASB as a post-treatment step for catalytically oxidized OMW is recommended.     

EPS and SMP dynamics at different heights of a submerged anaerobic membrane bioreactor (SAMBR)

Membrane bioreactors (MBR) technology for wastewater offers many advantages over conventional technologies such as high effluent quality, less footprint and others. The main disadvantage of membrane bioreactors (MBR) is related to membrane fouling, which is mainly caused by extracellular polymeric substance (EPS) and soluble microbial products (SMP). This research studied EPS and SMP dynamics at different heights of a submerged anaerobic membrane bioreactor (SAMBR). The SAMBR was operated under two organic loading rates (OLR) (0.79 and 1.56 kg/m³ d) and was fed with synthetic wastewater with glucose as the carbon source. The results showed percentages of chemical oxygen demand (COD) removal above 95% and the highest COD removal rates were observed at the bottom of the reactor (>83%) for both OLR. The EPS showed a stratification with highest quantities in the supernatant. For the SMP the highest concentration was in the bottom of SAMBR where utilization predominated associated products whereas in the SAMBR supernatant predominated biomass associated products. The OLR change led to a significant increase in SMP accumulation but not in EPS. These facts showed that EPS and SMP dynamic in the SAMBR seemed to be mainly influenced by biological activity, total suspended solids concentration and substrate composition.     

Impact of crop species on bacterial community structure during anaerobic co-digestion of crops and cow manure

The bacterial communities in three continuously stirred tank reactors co-digesting cow manure with grass silage, oat straw, and sugar beet tops, respectively, were investigated by 16S rRNA gene-based fingerprints and clone libraries. The analyses revealed both clearly distinct and similar phylotypes in the bacterial communities between the reactors. The major groups represented in the three reactors were Clostridia, unclassified Bacteria, and Bacteroidetes. Phylotypes affiliated with Bacilli or Deltaproteobacteria were unique to the sugar beet and straw reactor, respectively. Unclassified Bacteria dominated in sugar beet reactor while in the straw and grass reactor Clostridia was the dominant group. An increase in organic loading rate from 2 to 3 kg volatile solids m^?3 d^?1 resulted in larger changes in the bacterial community in the straw compared to grass reactor. The study shed more light on the evolution of bacterial community during anaerobic co-digestion of different crops and manure to methane.     

An industrial level system with nonisothermal simultaneous solid state saccharification,fermentation and separation for ethanol production

To alleviate the problems of low substrate loading, nonisothermal, end-product inhibition of ethanol during the simultaneous saccharification and fermentation, a nonisothermal simultaneous solid state saccharification, fermentation, and separation (NSSSFS) process was investigated; one novel pilot scale nonisothermal simultaneous solid state enzymatic saccharification and fermentation coupled with CO₂ gas stripping loop system was invented and tested. The optimal pretreatment condition of steam-explosion was 1.5 MPa for 5 min in industrial level. In the NSSSFS, enzymatic saccharification and fermentation proceeded at around 50 °C and 37 °C, respectively, and were coupled together by the hydrolyzate loop; glucose from enzymatic saccharification was timely consumed by yeast, and the formed ethanol was separated online by CO₂ gas stripping coupled with adsorption of activated carbon; the solids substrate loading reached 25%; ethanol yields from 18.96% to 30.29% were obtained in fermentation depending on the materials tested. Based on the pilot level of 300 L fermenter, a novel industrial-level of 110 m³ solid state enzymatic saccharification, fermentation and ethanol separation plant had been successfully established and operated. The NSSSFS was a novel and feasible engineering solution to the inherent problems of simultaneous saccharification and fermentation, which would be used in large scale and in industrial production of ethanol.     

Co-digestion of cow manure,food waste and intermittent input of fat

Pulses of oil were added to completely mixed reactors fed with dairy cow manure and food waste, after achieving a stable performance at an organic loading rate of 4.6 ± 0.1 gCOD/(l_reactor day), an oily waste effluent from a canned fish processing industry was fed in the form of pulses. The oil concentration rose up to 9, 12, 15 and 18 gCOD_oil/l_reactor, after the pulse feeding in the reactor. The highest fat concentration of 18 gCOD_oil/l_reactor promoted a persistent inhibition in the process of the continuous reactor, although in batch assays, the reactor content evidenced a capacity to degrade more oil and to degrade the accumulated organic matter. All the other pulses had a positive effect in the methane production. From a practical point of view, this work demonstrates that controlled intermittent inputs of oil can enhance the methane production in a co-digestion of cow manure and food waste.     

Anaerobic Digestion of Dairy Manure in a Hybrid Reactor with Biogas Recirculation

Summary A novel anaerobic hybrid reactor (AHR) configuration incorporating floating support media for biomass immobilization and biogas recirculation for enhanced mixing was used for anaerobic digestion of dairy manure. No pretreatment or solid liquid separation was applied. The reactor was operated at high influent volatile solids (VS) and organic loading rates (OLR) of up to 9.87% and 7.30 g VS/l day, respectively. After 149 days of continuous operation the results revealed that a high amount (38.1 g VSS) of biomass was able to attach itself to the support medium being used. The investigated AHR configuration achieved COD, BOD, TS, and VS removal efficiencies of 48–63, 64–78, 55–65, and 59–68%, respectively, at a hydraulic retention time (HRT) of 15 days. The corresponding average methane production value obtained in this study was 0.191 l/g VS added.     

Operation of an aerobic granular pilot scale SBR plant to treat swine slurry

A pilot-scale Sequencing Batch Reactor was operated during 307 days in order to treat swine slurry characterized by its high variable composition: organic and nitrogen applied loading rates and C/N ratio were 1.4–6.3 kg COD_s/(m³ d), 0.5–2.5 kg N/(m³ d) and 1.9–9.4 g COD_s/(g N), respectively. Aerobic granules successfully developed in the reactor and their physical properties remained rather stable despite the feeding composition variability. Organic and ammonia removal efficiency reached 61–73% and 56–77%, respectively, however ammonia was mainly oxidized to nitrite. The reactor had a good biomass retention capacity to select for granular biomass. However, its efficiency to retain the solids present in the feeding was low. Aerobic granulation in SBR systems appears as an interesting alternative to treat slurry in small livestock facilities where the implementation of anaerobic digestion systems is not a feasible option or the removal of nitrogenous compounds is required.     

Microbial communities involved in biogas production from wheat straw as the sole substrate within a two-phase solid-state anaerobic digestion

Microbial communities involved in biogas production from wheat straw as the sole substrate were investigated. Anaerobic digestion was carried out within an up-flow anaerobic solid-state (UASS) reactor connected to an anaerobic filter (AF) by liquor recirculation. Two lab-scale reactor systems were operated simultaneously at 37 °C and 55 °C. The UASS reactors were fed at a fixed organic loading rate of 2.5 g L⁻¹ d⁻¹, based on volatile solids. Molecular genetic analyses of the bacterial and archaeal communities within the UASS reactors (digestate and effluent liquor) and the AFs (biofilm carrier and effluent liquor) were conducted under steady-state conditions. The thermophilic UASS reactor had a considerably higher biogas and methane yield in comparison to the mesophilic UASS, while the mesophilic AF was slightly more productive than the thermophilic AF. When the thermophilic and mesophilic community structures were compared, the thermophilic system was characterized by a higher Firmicutes to Bacteroidetes ratio, as revealed by 16S rRNA gene (rrs) sequence analysis. The composition of the archaeal communities was phase-separated under thermophilic conditions, but rather stage-specific under mesophilic conditions. Family- and order-specific real-time PCR of methanogenic Archaea supported the taxonomic distribution obtained by rrs sequence analysis. The higher anaerobic digestion efficiency of the thermophilic compared to the mesophilic UASS reactor was accompanied by a high abundance of Firmicutes and Methanosarcina sp. in the thermophilic UASS biofilm.     

Anaerobic digestion of harvested aquatic weeds: water hyacinth (Eichhornia crassipes), cabomba (Cabomba Caroliniana) and salvinia (Salvinia molesta)

The aim of this study was to explore the potential of three aquatic weeds, water hyacinth, cabomba, and salvinia, as substrates for anaerobic digestion. A set of four pilot-scale, batch digestions were undertaken to assess the yield and quality (% methane) of biogas from each plant species, and the rate of degradation. A set of 56 small-scale (100 mL) biological methane potential (BMP) tests were designed to test the repeatability of the digestions, and the impact of drying and nutrient addition.The results of the pilot-scale digestions show that both water hyacinth and cabomba are readily degradable, yielding 267 L biogas kg^?1 VS and 221 L biogas kg^?1 VS, respectively, with methane content of approximately 50%. There is evidence that the cabomba fed reactor leaked midway through the digestion therefore the biogas yield is potentially higher than measured in this case. Salvinia proved to be less readily degradable with a yield of 155 L biogas kg^?1 VS at a quality of 50% methane.The BMPs showed that the variability was low for water hyacinth and cabomba but high for salvinia. They also showed that the addition of nutrient solution and manure did not significantly increase the biogas yields and that drying was detrimental to the anaerobic degradability of all three substrates.Based on these results treatment of both water hyacinth and cabomba by anaerobic digestion can be recommended. Anaerobic digestion of Salvinia cannot be recommended due to the low biogas yields and high variability for this substrate.     

Alkalinity ratios to identify process imbalances in anaerobic digesters treating source-sorted organic fraction of municipal wastes

Two 5 L anaerobic reactors were used to monitor the mesophilic anaerobic digestion of source sorted organic fraction of municipal solid wastes (SS-OFMSW) focusing the attention on the response of alkalinity ratios. Intermediate/partial alkalinity (IA/PA) ratio can be used as a simple and cheaper alternative to VFAs analysis when digester's stability needs to be assessed in full-scale plants treating these organic wastes. However, lab-scale studies in order to establish a specific limit value of IA/PA referred to SS-OFMSW had not been conducted. In this study, a reference reactor (R1) was operated at low organic loading rates (OLR) and high hydraulic retention times (HRT) during 165 days. Besides, severe disturbances were applied to a second reactor (R2) during 281 days by means of increasing both HRT and OLR in order to assess the digester response under continuous overload conditions. The obtained results show that an IA/PA ratio of below 0.3 is recommended to maintain total VFAs between 2.5 and 3.5 kg m⁻³ and achieve a stable reactor performance treating SS-OFMSW in a range of total alkalinity (TA) between 13 and 15 kg CaCO₃ m⁻³. These results provide a starting point to develop further works in full-scale digesters, in order to improve the monitoring and process control of full-scale anaerobic reactors treating SS-OFMSW.     

Bench-scale fermentation of Trichoderma viride on wastewater sludge: Rheology,lytic enzymes and biocontrol activity

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 10⁷ CFU mL⁻¹ at 96 h) was obtained at 30 g L⁻¹ suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L⁻¹ suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL⁻¹ at 30 g L⁻¹ suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L⁻¹ compared to 30 and 25 g L⁻¹. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, k_La at 35 g L⁻¹ did not increase in comparison to 30 g L⁻¹ due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.     

The effect of organic loading rate and retention time on hydrogen production from a methanogenic CSTR

The possibility of shifting a methanogenic process for hydrogen production by changing the process parameters viz., organic loading rate (OLR) and hydraulic retention time (HRT) was evaluated. At first, two parallel semi-continuously fed continuously stirred tank reactors (CSTR) were operated as methanogenic reactors (M1 and M2) for 78 days. Results showed that a methane yield of 198-218 L/kg volatile solids fed (VS(fed)) was obtained when fed with grass silage at an OLR of 2 kgVS/m3/d and HRT of 30 days. After 78 days of operation, hydrogen production was induced in M2 by increasing the OLR from 2 to 10 kgVS/m3/d and shortening the HRT from 30 to 6 days. The highest H? yield of 42 L/kgVS(fed) was obtained with a maximum H? content of 24%. The present results thus demonstrate that methanogenic process can be shifted towards hydrogen production by increasing the OLR and decreasing HRT.     

Effect of by-product gypsum application rate to grass pasture,grass hay,and corn silage on fermentation by rumen microorganisms in continuous culture

A dual-flow continuous culture fermenter system was used to investigate ruminal fermentation in response to increased by-product gypsum application rate of three forages. The treatments included 0, 22, 45, and 90 tonnes/ha by-product gypsum applied to grass plots and 0, 22, and 45 tonnes/ha by-product gypsum applied to corn plots. Forage was harvested to represent grass pasture (GP), grass hay (GH), and corn silage (CS), dried, ground, and fed to fermenters at a rate of 60 g dry matter (DM)/day. Organic matter (OM) and neutral detergent fiber (aNDF) digestibilities, rumen pH, total volatile fatty acid (VFA) production, and N metabolism were not affected by gypsum application rate for all forage types. The GH had greater sulfur content than recommended as the maximum tolerable level by the National Research Council (NRC). The results of this study indicate that ruminal fermentation was not compromised when by-product gypsum was applied to GP, GH, or CS at rates up to 90 tonnes/ha. By-product gypsum application to pastures and crops shows promise as an economical soil amendment to reduce dissolved phosphorus loss in runoff, although potential animal health issues should be further evaluated.     

Anaerobic digestion of processed municipal solid waste using a novel high solids reactor: Maximum solids levels and mixing requirements

Summary Novel, laboratory-scale, high solids reactors operated under mesophilic conditions were used to study the anaerobic fermentation of processed municipal solid waste (MSW) to methane. The anaerobic digestion consortium was introduced to high solids levels through gradual adaptation. The maximum sludge solids level for stable anaerobic fermentation performance was identified as approximately 36% wt/wt. Recovery of the anaerobic consortium, following dilution of inhibitory high solids levels, was swift. Reactor mixing requirements were also studied. No significant difference in fermentation performance was observed between agitator speeds of 1 and 25 rpm. Preliminary fermentation performance tests showed that solids loading rates as high as 9.5 g VS (volatile solids) feed/L sludge^.d, at 32% solids within the reactor, were possible. Under these conditions, operation was stable with an average pH of 7.8–8.0, total volatile fatty acid pools of <20 mM, and a biogas composition of 55%–60% methane.     

Synthesis of biodiesel in column fixed-bed bioreactor using the fermented solid produced by Burkholderia cepacia LTEB11

We produced a lipase from Burkholderia cepacia in solid-state fermentation and used it to catalyze the synthesis of biodiesel in a fixed-bed reactor. In the solid-state fermentation step, a 50:50 (by mass) mixture of sugarcane bagasse and sunflower seed meal gave 234 units of pNPP-hydrolyzing activity per gram of dry solids at 96 h. This fermented solid was lyophilized and delipidated, packed into a column and used to catalyze the synthesis of biodiesel through the ethanolysis of soybean oil in a medium free of co-solvents, with the reaction mixture being continuously circulated through the column. The best conversion was 95% after 46 h, which was obtained at 50 °C, with an alcohol:oil molar ratio of 3:1, alcohol addition in two steps and the addition of 1% of (m/m) water to the reaction medium. This system has potential to decrease the costs of enzyme-catalyzed transesterification reactions.     

Treatment of fresh leachate with high-strength organics and calcium from municipal solid waste incineration plant using UASB reactor

Treatment of a fresh leachate with high-strength organics and calcium from municipal solid waste (MSW) incineration plant by an up-flow anaerobic sludge blanket (UASB) reactor was investigated under mesophilic conditions, emphasizing the influence of organic loading rate (OLR). When the reactor was fed with the raw leachate (COD as high as 70,390-75,480 mg/L) at an OLR of 12.5 kg COD/(m³ d), up to ∼82.4% of COD was removed suggesting the feasibility of UASB process for treating fresh leachates from incineration plants. The ratio of volatile solids/total solids (VS/TS) of the anaerobic sludge in the UASB decreased significantly after a long-term operation due to the precipitation of calcium carbonate in the granules. Scanning electron microscopy (SEM) observation shows that Methanosaeta-like species were in abundance, accompanied by a variety of other species. The result was further confirmed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing.     

The effect of sulfate reduction on the thermophilic (55°C) methane fermentation process

Summary The continuously operated suspended growth anaerobic contact system was utilized to estimate the effect of sulfate reduction on the thermophilic (55°C) methane fermentation process. Results indicated that reduction in methanogenesis in the presence of sulfate was due to two separate, but related, processes;i.e. competitive and sulfide inhibition. Although prevention of competitive inhibition would be difficult under normal fermenter operation, sulfide inhibition could be minimized by environmental selection of sulfide tolerant microbial populations through biomass recycle and pH control. Stable fermenter operation was achieved at soluble sulfide concentrations as high as 330 mg/l soluble sulfide. Using batch fermenters, a maximum thermophilic sulfate reduction rate of 3.7 mg SO₄ ^2––S/g volatile solids (VS)-day was estimated. The importance of reporting sulfate reduction rates on a biomass basis is demonstrated by a simple population adjustment kinetic model.This research study was conducted at the Department of Agricultural Engineering, Cornell University, Riley Robb Hall, Ithaca, NY 14853, U.S.A.