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

A review on biogas upgrading in anaerobic digestion systems treating organic solids and wastewaters via biogas recirculation

Biogas upgrading is an essential process for efficient and safe utilization of biogas produced from anaerobic digestion (AD), a cost-effective and environmentally friendly technology for bioenergy recovery from organic wastes. Biogas recirculation in AD reactors has been recently reported as a cost-effective and promising method to enhance methane content in biogas. This review aimed to summarize the state-of-the-art of biogas recirculation-based AD systems to better understand the possible mechanisms and main factors relating to in-situ biogas upgrading. It shows that biogas recirculation in the AD reactor can not only enhance methane content via both physicochemical and biological effects, but also help establish a robust AD system with high buffering capacity for highly efficient treatment of various organic wastes. More research works are demanding for a better understanding of the mechanisms and the optimization of the whole AD system, targeting its further development for high-calorie bioenergy production.

Coupling biogas recirculation with FeCl3 addition in anaerobic digestion system for simultaneous biogas upgrading, phosphorus conservation and sludge conditioning

The high costs involved in sewage sludge treatment and disposal in wastewater treatment plants (WWTPs) not only bring about improper sludge disposal and thus environmental pollutions, but also limit the investment on construction of WWTPs, especially in rural areas or low-income regions. This comparative study examined the effect of biogas recirculation coupled with chemical addition in a semi-continuous anaerobic digester for sludge treatment, which was proven to achieve biogas upgrading, phosphorus conservation and sludge conditioning simultaneously, largely reducing the sludge treatment cost. Results show that FeCl₃ addition coupling biogas recirculation can improve sludge dewaterability by 94% in comparison to 75% by equivalent MgCl₂ addition, and 97% phosphorus in digestate can be conserved in solid with formation of vivianite-like crystals. Biogas recirculation can enhance CH₄ yield and content by 13% and 11%, respectively, likely attributable to the increased relative abundances of both hydrogenotrophic Methanomicrobiales and acetoclastic Methanosarcinales.

Waste Management in Dairy Cattle Farms in Aydın Region. Potential of Energy Application

In this paper, the dairy cattle waste management systems on farms in Aydın region in Turkey were investigated. Number of farms and livestock herd size, type of barn, type of machinery and farm labour force were studied. The collection, management and storage systems of manure produced in dairy cattle farms were taken into consideration. Additionally, biogas amount, which is produced from animal waste, was calculated for all districts of Aydın by using the number of livestock animals and various criteria such as the rate of dry matter. Results show that the typical and representative farm in the Aydın region is facility with a total head over 100 heads. 89.6% of the farms have heads in the range of 100 to 200. The amount of biogas that can be produced from all manure collected in Aydın region in the biogas plants is approximately 160,438 m3/day (based on 0.5 m3/day biogas per cattle), which would produce around 100 GWh/year that can be used for own needs of farms owners.

Determination of optimum electrical connection mode for multi-electrode-embedded microbial fuel cells coupled with anaerobic digester for enhancement of swine wastewater treatment efficiency and energy recovery

In this work, three multi-electrode-embedded microbial fuel cells (MFCs) were connected sequentially and operated in series and parallel modes, fed by effluent of an anaerobic digester continuously operated using swine wastewater. The anaerobic digester achieved ~0.75 CH₄ L d^-1 while removing 71.2% of COD and 0.8% of ammonia, which was comparable to the literatures reported. The MFCs removed additional COD from the anaerobic digester effluent, achieving the lowest concentration in the last unit, leading to a voltage reversal in the serially-connected unit. The MFCs connected and operated in parallel mode showed the highest power density of ~25 W m^-3, which is 18% higher compared to the one operated in series mode. These results definitively show that differences in substrate concentrations among MFC units are inevitable with sequential flow. Further, a parallel connection mode of operation is necessary to achieve stable, long-term power generation from MFC units, without any electrical malfunction.

High-rate anaerobic treatment of digestate using fixed film reactors

The effluent stream of the anaerobic digestion processes, the digestate, accommodates high residual organic content that needs to be further treated before discharge. Anaerobic treatment of digestate would not only reduce the residual organic compounds in digestate but also has a potential to capture the associated biogas. High-rate anaerobic reactor configurations can treat the waste streams using lower hydraulic retention times which requires less footprint opposed to the conventional completely stirred tank reactors. This study investigated the high-rate anaerobic treatment performance and the associated biogas capture from the digestate of a manure mixture composed of 90% laying hen and 10% cattle manures in fixed-film reactors. The results indicated that it was possible to reduce total chemical oxygen demand content of the digestate by 57-62% in 1.3-1.4 days of hydraulic retention time. The corresponding biogas yields obtained were in the range of 0.395-0.430 L_biogas/g VS_added which were found to be comparable to many raw feedstocks. Moreover, significant total phosphorus reduction (36-47%) and greenhouse gas capture (over 14.5-18.1 tCO₂e/d per m³ digestate) were also recorded in the anaerobic fixed-film reactors.

Performance evaluation of anaerobic hybrid reactors with different packing media for treating wastewater of mild alkali treated rice straw in ethanol fermentation process

Four anaerobic hybrid reactors with different packing media viz. gravel (R1), pumice stone (R2), polypropylene saddles (R3) and ceramic saddles (R4) were operated in semi-continuous mode. Biomethanation potential of the wastewater generated during alkali-treatment of rice straw in ethanol production process was investigated at ambient conditions. The reactors were operated with varying organic loading rates (0.861-4.313 g COD l(-1) d(-1)) and hydraulic retention time (3-15 days). Higher COD removal efficiency (69.2%) and methane yield (0.153 l CH4 g(-1) CODadded) were achieved in reactor R2 at 15 days HRT. Modified Stover-Kincannon model was applied to estimate the bio-kinetic coefficients and fitness of the model was checked by the regression coefficient for all the reactors. The model showed an excellent correlation between the experimental and predicted values. The present study demonstrated the treatment of wastewater from alkali treated rice straw for production of biogas.

Kinetics of psychrophilic anaerobic sequencing batch reactor treating flushed dairy manure

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.

Performance of anaerobic hybrid reactors for the treatment of complex phenolic wastewaters with biogas recirculation

This study investigates the application of a novel anaerobic hybrid reactor (AHR) configuration, incorporating support media for biomass immobilisation and biogas recirculation for improved mixing towards the anaerobic treatment of complex phenolic wastewater. Synthetic coal wastewater with an average phenolics and COD concentration of 752 and 2240 mg L(-1) was used as substrate. Biogas recirculation was employed at four different rates of 11.25, 16.87, 25.30 and 37.95 L d(-1) for 100 days. Phenolics and COD removal improved with increase in biogas recirculation. After 120 days of continuous operation, the results revealed that a high amount (14.0 g VSS) of biomass was able to attach itself to the support medium. The investigated AHR configuration achieved phenolics and COD removal efficiencies of 95% and 92% respectively at a hydraulic retention time (HRT) of 0.33 d. The corresponding average methane production obtained in this study was 0.02 mol methane g(-1) COD.

Modification of a conventional anaerobic digester for improving the effluent and sludge characteristics

The aim of this study was to enrich the composition of anaerobic digester sludge in terms of nitrogen and phosphorus by struvite (MgNH4PO4) formation. Waste activated sludge was anaerobically digested in batch reactors under the conditions that the minimum stoichiometric requirement for struvite formation was satisfied in all reactors. For this purpose, different amounts of magnesium (Mg2+) and phosphate (PO4(3-)) ions were added initially to the batch reactors. The results showed the effects of adding Mg2+ and PO4(3-) ions on the performance of anaerobic digestion and on the amounts of ammonium (NH4+) and PO4(3-) ions released during digestion. The results indicated that the performance of the anaerobic digestion in chemical oxygen demand removal changed between -4.0% and 15.4% for a Mg2+ concentration range of 277.2 to 529.3 mg/L and a PO4(3-) concentration range of 377.4 to 2372.4 mg/L. There was an increase in the concentration of NH4+ in all reactors during digestion, but the extent of concentration increase could be controlled by increasing the initial concentrations of Mg2+ and PO4(3-). The maximum removal of NH4+ ions (33.7%) was observed in the reactor dosed initially by Mg2+ and PO4(3-) concentrations of 467.2 and 2123.3 mg/L, respectively. The concentration of PO4(3-) ion was lower than its initial concentration in all reactors, indicating considerable fixation of PO4(3-) as it was released, by struvite and other solid species formation. The decrease in the concentration of Mg2+ ions similar to PO4(3-) was accepted as evidence for the formation of solid species composed of Mg2+ and PO4(3), in addition to struvite. Water

Removal of ammonium and phosphate from the supernatant of anaerobically digested waste activated sludge by chemical precipitation

The removal of ammonium (NH(4)(+)) and phosphate (PO(4)(3-)) from supernatant of anaerobic digestion by magnesium ammonium phosphate (MAP) formation was studied. To be able to find out the loss of NH(4)(+) by its transformation to NH(3), rates of NH(4)(+) removal by aeration and by MAP formation combined with aeration were compared. NH(4)(+) removal by aeration was found to be insignificant. The kinetics of MAP formation was fast. The removal rate of NH(4)(+) and Mg(2+) was the smallest and the largest, respectively based on rate constants calculated. The removal of NH(4)(+) showed sensitivity to Mg(2+) and PO(4)(3-) concentrations and controlled the purity of MAP precipitate. The removal of PO(4)(3-) was found to be sensitive to mainly Mg(2+) ion. These results also indicated that as the supernatant solution became more saturated in terms of MAP forming ions, the effect of pH increase became insignificant in the removal of ions from the solution.

Decolorization and COD reduction of UASB pretreated poultry manure wastewater by electrocoagulation process: a post-treatment study

The performance of electrocoagulation (EC) technique for decolorization and chemical oxygen demand (COD) reduction of anaerobically pretreated poultry manure wastewater was investigated in a laboratory batch study. Two identical 15.7-L up-flow anaerobic sludge blanket (UASB) reactors were first run under various organic and hydraulic loading conditions for 216 days. Effects of operating parameters such as type of sacrificial electrode material, time of electrolysis, current density, initial pH, and electrolyte concentration were further studied to optimize conditions for the post-treatment of UASB pretreated poultry manure wastewater. Preliminary tests conducted with two types of sacrificial electrodes (Al and Fe) resulted that Al electrodes were found to be more effective for both COD and color removals than Fe electrodes. The subsequent EC tests performed with Al electrodes showed that optimal operating conditions were determined to be an initial pH of 5.0, a current density of 15mA/cm(2), and an electrolysis time of 20min. The results indicated that under the optimal conditions, about 90% of COD and 92% of residual color could be effectively removed from the UASB effluent with the further contribution of the EC technology used as a post-treatment unit. In this study, the possible acute toxicity of the EC effluent was also evaluated by a static bioassay test procedure using guppy fish (Lebistes reticulatus). Findings of this study clearly indicated that incorporation of a toxicological test into conventional physicochemical analyses provided a better evaluation of final discharge characteristics.

Anaerobic digestion technology in poultry and livestock waste treatment--a literature review

A literature review has been undertaken to investigate the performance of the different anaerobic process configurations and operational conditions used in poultry and livestock waste treatment. The results of the extensive literature review showed that a wide range of different reactor volumes varying from 100 mL to 95 m3 were utilized in the investigation of anaerobic processing of poultry manure. Retention times studied were between 13.2 h and 91 days. Most of studies were carried out under mesophilic conditions maintained between 25 and 35 degrees C. Chemical oxygen demand (COD) removals and organic loading rate (OLR) ranged from 32 to 78%, and from 1.1 to 2.9 kg COD m(-3) day(-1), respectively. Biogas yields were achieved between 180 mL g(-1) COD added and 74 m3 day(-1) for a wide range of different reactor configurations. Up-flow anaerobic sludge blanket (UASB) seems to be a suitable process for the treatment of poultry manure wastewater and the liquid fraction of hen manure, due to its ability to maintain a sufficient amount of active biomass. The literature review showed that various reactor configurations such as fixed-film reactor, attached-film bioreactor, anaerobic rotating biological reactor, batch reactors, downflow anaerobic filter, fixed dome plant, UASB, continuously stirred tank reactor (CSTR), up-flow anaerobic filter (UAF), temperature-phased anaerobic digestion (TPAD), anaerobic hybrid reactor (AHR), and two-stage anaerobic systems are well suited to anaerobic processing of cattle manure. At both mesophilic and thermophilic conditions, high COD removals (87-95%) were achieved for treatment of cattle manure wastewaters. The COD and volatile solids (VS) reductions obtained were 37.9 to 94% and 9.6 to 92%, respectively. During the studies, OLR and retention times ranged between 0.117 and 7.3 g VS L(-1) day(-1) and between 0.5 and 140 days, respectively. In anaerobic processing of cattle manure, methane yields between 48 mmol CH4 L(-1) and 4681.3 m3 CH4 month(- 1) were found for the corresponding reactor volumes of 120 mL and 1300 m3, respectively. In anaerobic processing of swine manure, OLR ranged from 0.9 to 15.42 g VS L(-1) day(- 1) at mesophilic conditions (25-35 degrees C). The reactor volumes varied between 125 mL and 380 L. Temperature and retention times ranged from 25 to 60 degrees C, and 0.9 to 113 days, respectively. COD and VS reductions achieved were between 57 and 78% and between 34.5 and 61%, respectively. Moreover, methane yields were obtained between 22 and 360 mL CH4 g(-1) VS added. The results showed that UASB, anaerobic baffled reactors, CSTR, and anaerobic sequencing batch reactor (ASBR) were successfully utilized in anaerobic processing of swine manure at both mesophilic and thermophilic conditions.

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.

Development of empirical models for performance evaluation of UASB reactors treating poultry manure wastewater under different operational conditions

A nonlinear modeling study was carried out to evaluate the performance of UASB reactors treating poultry manure wastewater under different organic and hydraulic loading conditions. Two identical pilot scale up-flow anaerobic sludge blanket (UASB) reactors (15.7 L) were run at mesophilic conditions (30-35 degrees C) in a temperature-controlled environment with three hydraulic retention times (theta) of 15.7, 12 and 8.0 days. Imposed volumetric organic loading rates (L(V)) ranged from 0.65 to 4.257 kg COD/(m(3) day). The pH of the feed varied between 6.68 and 7.82. The hydraulic loading rates (L(H)) were controlled between 0.105 and 0.21 m(3)/(m(2)day). The daily biogas production rates ranged between 4.2 and 29.4 L/day. High volumetric COD removal rates (R(V)) ranging from 0.546 to 3.779 kg COD(removed)/(m(3)day) were achieved. On the basis of experimental results, two empirical models having a satisfactory correlation coefficient of about 0.9954 and 0.9416 were developed to predict daily biogas production (Q(g)) and effluent COD concentration (S(e)), respectively. Findings of this modeling study showed that optimal COD removals ranging from 86.3% to 90.6% were predicted with HRTs of 7.9, 9.5, 11.2, 12.6, 13.7 and 14.3 days, and L(V) of 1.27, 1.58, 1.78, 1.99, 2.20 and 2.45 kg COD/(m(3)day) for the corresponding influent substrate concentrations (S(i)) of 10,000, 15,000, 20,000, 25,000, 30,000 and 35,000 mg/L, respectively.

Improvement of COD and color removal from UASB treated poultry manure wastewater using Fenton's oxidation

The applicability of Fenton's oxidation as an advanced treatment for chemical oxygen demand (COD) and color removal from anaerobically treated poultry manure wastewater was investigated. The raw poultry manure wastewater, having a pH of 7.30 (+/-0.2) and a total COD of 12,100 (+/-910) mg/L was first treated in a 15.7 L of pilot-scale up-flow anaerobic sludge blanket (UASB) reactor. The UASB reactor was operated for 72 days at mesophilic conditions (32+/-2 degrees C) in a temperature-controlled environment with three different hydraulic retention times (HRT) of 15.7, 12 and 8.0 days, and with organic loading rates (OLR) between 0.650 and 1.783 kg COD/(m3day). Under 8.0 days of HRT, the UASB process showed a remarkable performance on total COD removal with a treatment efficiency of 90.7% at the day of 63. The anaerobically treated poultry manure wastewater was further treated by Fenton's oxidation process using Fe2+ and H2O2 solutions. Batch tests were conducted on the UASB effluent samples to determine the optimum operating conditions including initial pH, effects of H2O2 and Fe2+ dosages, and the ratio of H2O2/Fe2+. Preliminary tests conducted with the dosages of 100 mg Fe2+/L and 200 mg H2O2/L showed that optimal initial pH was 3.0 for both COD and color removal from the UASB effluent. On the basis of preliminary test results, effects of increasing dosages of Fe2+ and H2O2 were investigated. Under the condition of 400 mg Fe2+/L and 200 mg H2O2/L, removal efficiencies of residual COD and color were 88.7% and 80.9%, respectively. Under the subsequent condition of 100 mg Fe2+/L and 1200 mg H2O2/L, 95% of residual COD and 95.7% of residual color were removed from the UASB effluent. Results of this experimental study obviously indicated that nearly 99.3% of COD of raw poultry manure wastewater could be effectively removed by a UASB process followed by Fenton's oxidation technology used as a post-treatment unit.

Anaerobic digestion of dairy manure with enhanced ammonia removal

Poor ammonia-nitrogen removal in methanogenic anaerobic reactors digesting animal manure has been reported as an important disadvantage of anaerobic digestion (AD) in several studies. Development of anaerobic processes that are capable of producing reduced ammonia-nitrogen levels in their effluent is one of the areas where further research must be pursued if AD technology is to be made more effective and economically advantageous. One approach to removing ammonia from anaerobically digested effluents is the forced precipitation of magnesium ammonium phosphate hexahydrate (MgNH4PO4 x 6H2O), commonly called struvite. Struvite is a valuable plant nutrient source for nitrogen and phosphorus since it releases them slowly and has non-burning features because of its low solubility in water. This study investigated coupling AD and controlled struvite precipitation in the same reactor to minimize the nitrogen removal costs and possibly increase the performance of the AD by reducing the ammonia concentration which has an adverse effect on anaerobic bacteria. The results indicated that up to 19% extra COD and almost 11% extra NH3 removals were achieved relative to a control by adding 1750 mg/L of MgCl2 x 6H2O to the anaerobic reactor.