Anaerobic Digestion Of Dairy Manure Research Articles

Enhancing the Performance of Anaerobic Digestion of Dairy Manure through Phase‐Separation

AbstractAnaerobic digestion (AD) is an effective way to convert animal manures into profitable by‐products while simultaneously reducing the pollution of water, air, and soil caused by these wastes. Conventional high‐rate anaerobic reactors cannot effectively process animal manures with high solids‐containing wastes. The two‐phase configuration for AD has several advantages over conventional one‐phase processes, e. g., increased stability of the process, smaller size and cost efficient process configurations. In the present study, the experiments were carried out in a two‐phase system composed of an acidogenic reactor and a methanogenic reactor, and in a one‐phase system composed of only a methanogenic reactor. The reactors were operated as unmixed (without an external mixing aid), unsophisticated, and daily‐fed mode. It was found that the two‐phase configuration was more efficient than the one‐phase system. The biogas production in the two‐phase system at a hydraulic retention time (HRT) of 8.6 days (only methanogenic phase) was calculated to be 42% higher at an organic loading rate (OLR) of 3.5 g VS/L·day than that of the one‐phase with a HRT of 20 days. This translates into significant performance improvement and reduced volume requirement. This finding represents a further step in the achievement of wider use of simple anaerobic reactor configurations for waste treatment in rural areas.

Phosphorus forms and extractability in dairy manure: A case study for Wisconsin on-farm anaerobic digesters

The effect of anaerobic digestion on phosphorus (P) forms and water P extractability was investigated using dairy manure samples from six full-scale on-farm anaerobic digesters in Wisconsin, USA. On an average, total dissolved P (TDP) constituted 12 ± 4% of total P (TP) in the influent to the anaerobic digesters. Only 7 ± 2% of the effluent was in a dissolved form. Dissolved unreactive P (DUP), comprising polyphosphates and organic P, dominated the dissolved P component in both the influent and effluent. In most cases, it appeared that the fraction of DUP mineralized during anaerobic digestion became subsequently associated with particulate-bound solids. Geochemical equilibrium modeling with Mineql+ indicated that dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, octacalcium phosphate, newberyite, and struvite were the probable solid phases in both the digester influent and effluent samples. The water-extractable P (WEP) fraction in undigested manure ranged from 45% to 70% of TP, which reduced substantially after anaerobic digestion to 25% to 45% of TP. Anaerobic digestion of dairy manure appears capable of reducing the fraction of P that is immediately available by increasing the stability of the solid phases controlling P solubility.

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 (MgNH 4PO 4·6H 2O), 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 NH 3 removals were achieved relative to a control by adding 1750 mg/L of MgCl 2·6H 2O to the anaerobic reactor.

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

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.

Electrochemical oxidation of the effluent from anaerobic digestion of dairy manure

The electrochemical oxidation of the digested effluent from anaerobic digestion of dairy manure was investigated in this study. The digested effluent sample containing with suspended solids was pretreated by filtration for the electrochemical experiment. The influence of direct anodic oxidation and indirect oxidation was evaluated through the use of dimensionally stable anode (DSA) and Ti/PbO 2 as anode. The decreasing rate of chemical oxygen demand (COD) was higher at lead dioxide coated titanium (Ti/PbO 2) electrode than at DSA, however the DSA was preferred anode for the decrease of ammonium nitrogen (NH 4-N) due to the control of ammonium nitrate (NO 3-N) accumulation. The results showed that the filtration of suspended solids as a pretreatment and addition of NaCl could improve the whole removing efficiency of NH 4-N in the digested effluent on electrochemical oxidation.

INFLUENCE OF ANAEROBIC DIGESTION ON DAIRY MANURE PHOSPHORUS EXTRACTABILITY

On-farm anaerobic treatment is used for solids, odor and pathogen removal, and energy recovery. Not much information is available on the effect of this treatment method on phosphorus (P) dynamics. The objective of this study was to investigate the effect of different inoculum-to-substrate ratios (ISR) on P extractability from anaerobically digested dairy manure. Dairy manure (substrate) and anaerobically digested dairy manure (inoculum) were collected from a full-scale on-farm anaerobic digester. High ISR (HIS, with ISR = 2.0) and low ISR (LIS, with ISR = 0.3) samples were prepared on a volatile solids (VS) basis. These samples were subjected to mesophilic (35°C) anaerobic digestion in batch reactors without mixing for 120 d. Specific methane yield, TS, and VS removal were higher in the LIS system compared to the HIS system. Serial and repeated extraction methods were used to characterize P extractability. De-ionized (DI) water and MgCl2 were used as extractants in the serial extraction method with extractant-to-manure ratios (EMR) ranging from 3 to 127. For repeated extraction, manure was extracted six times with DI water (EMR = 3). While anaerobic treatment decreased water-extractable P (WEP) in LIS extracts at EMR values of 3 and 7 by 28% and 24%, respectively, a significant increase (40%) in WEP occurred at an EMR of 3 at HIS. Water-extractable P in all other serial extracts of treated manure was higher than that in extracts of untreated manure regardless of ISR and EMR. Extractability of P increased sharply up to the third extraction step, after which it leveled off. The effectiveness of anaerobic digestion at LIS to reduce P extractability was also observed up to the second extraction step. In contrast, the digested manure always produced higher WEP levels for the HIS system. Our results indicate that, depending on the ISR used, anaerobic digestion of dairy manure can increase or decrease manure P extractability and, hence, its availability in runoff. However, it appears that this impact could be more pronounced under conditions where low runoff volumes are generated and for the first few precipitation events after land application of manure.

Effect of retention time and organic loading rate on anaerobic acidification and biogasification of dairy manure

AbstractVast amounts of animal manure produced from concentrated animal feeding operations have the potential to be converted into economic gain if the proper processing technology is employed. Anaerobic digestion (AD) is an effective way to convert organic wastes including animal manure into profitable by‐products as well as to reduce the pollution of water, air, and soil caused by these wastes. Two‐phase AD of manure offers several advantages over conventional one‐phase AD. Solids reduction through hydrolysis/acidification might be very significant for animal manure which contains high amounts of solids. However, to date, studies of two‐phase AD of animal manure have been limited to screened manure. Therefore, this study investigated the two‐phase AD of dairy manure with particular emphasis on the effects of retention time and organic loading rate (OLR) on anaerobic acidification and biogasification of unscreened dairy manure. The results indicated that pre‐acidification of dairy manure in daily‐fed continuously‐mixed reactors with no recycle led to significantly high reduction efficiencies of volatile solids and, thus, biogas production in the subsequent methanogenic reactor especially at OLRs of 4–10 g VS dm−3 day−1. However, the extent of the stimulation in the biogas production relative to corresponding feed samples was quite variable (between 6.9 and 64.7%) for different solids retention times and OLR combinations. A relatively lower performance was observed for the high OLRs (20–30 g VS dm−3 day−1) used which was attributed to the possible wash‐out of the acidifiers at the considerably low retention times (1.25–4 days) used. Copyright © 2004 Society of Chemical Industry

Attached-film media performance in psychrophilic anaerobic treatment of dairy cattle wastewater

Retention of microorganisms in anaerobic digesters by providing an attachment medium can potentially increase their productivity at lower operating temperatures. The objective of this work was to investigate the effectiveness of attached-film bioreactors for psychrophilic anaerobic digestion of dairy manure. Eight digesters were maintained in an environmental chamber, with the temperature varied between 37 and 10°C. Two digesters were packed with limestone gravel, two with pieces cut from non-woven polyester matting, two with a combination of limestone gravel and polyester pieces, and two had no packing. Digester operation was initiated at a temperature of 37°C. After the digesters reached stable operation at the initial temperature, the temperature was lowered slowly to 10°C. The temperature was held at 10°C for 5 weeks after stabilizing. The polyester medium with its high porosity and surface to volume ratio had the best overall performance for methane productivity at both 37 and 10°C. The biogas production (ml/d) and methane production (ml/d) were significantly higher for the polyester medium when compared to the limestone and combination media reactors ( p < 0.0001 and 0.0002, respectively). At 10°C, the polyester medium reactors performed significantly better than all others for biogas (ml/d) and methane (ml/d) production ( p < 0.0001). The polyester medium also yielded the maximum reductions in volatile solids (VS) and chemical oxygen demand (COD) at 37°C.

Performance Evaluation of Janata and Deenbandhu Biogas Plants

Performance of the Janata and Deenbandhu fixed dome biogas plants for anaerobic digestion of dairy manure was evaluated under the conditions of a hilly region. In contrast to Janata, the Deenbandhu biogas plant was found to be not only cheaper on the basis of cost / m3 rated capacity of the plant, but it also produced more gas per unit of manure fed and per unit of digester volume in addition to maintaining a consistent rate of gas production during subsequent years from initial charging. The higher production of gas by 28.5% and 12.5% per kg of manure fed and 49.5% and 28.9% per m3 of digester volume was observed from this plant for highest 24°C and lowest 14°C digester temperatures of the plants for the months of July and December respectively.

Anaerobic digestion of dairy manure and field crop residues

This research was undertaken to determine guidelines for combining dairy manure and field crop residues for maximum methane production per volume of anaerobic digester. The parameter investigated for establishing the proper mixture was the nonlignin-carbon to nitrogen ratio. Six 4·4 litre laboratory digesters, with operating volumes of 3·4 litre, were tested for 18 months with dairy cow manure combined with either barley straw, rice hulls or rice straw in three separate six-month phases. Non-lignin-carbon to nitrogen ratios of the various feed mixtures ranged between 12·3 and 40. Results indicate that methane production from fresh dairy manure can be enhanced by addition of chopped field crop residues. The maximum performance occurs when the non-lignin-carbon to nitrogen ratio of these feed mixtures is between 25 and 32. The non-lignin-carbon to nitrogen ratios for various other agricultural residues were also determined.

Effects of carbon: Nitrogen ratio on anaerobic digestion of dairy manure

This study is the initial phase of an investigation designed to supply criteria for combining various agricultural wastes to produce maximum methane per unit volume of an anaerobic digester. The parameter investigated for establishing proper mixtures of manure and carbonaceous waste was the ‘available-carbon to nitrogen’ ratio (C:N). Available-carbon was defined as the total organic carbon minus the lignin carbon. Six four-litre laboratory digesters were operated for 11 months. Screened dairy cow manure, which had a C:N ratio of 8·0, was combined with glucose and later in the experiment, cellulose, to obtain C:N ratios varying between 8·0 and 51·7. The loading rate was also varied: 1·0, 1·5 and 2·0 kg Volatile Solids m −3 day −1. With an increasing feed C:N ratio, the concentration of methane in the digester gas decreased (e.g. C: N = 8, CH 4 = 67%; C: N = 51·7, CH 4 = 51·7%). The greatest methane production per unit loading rate occurred when the C:N ratio of the feed was 25.