Downflow Anaerobic Filters Research Articles

Continuous treatment of dairy effluent in a downflow anaerobic filter packed with slag grains: Reactor performance and kinetics

ABSTRACT A downflow anaerobic filter packed with blast-furnace slag (BFS) grains was evaluated for treating cheese whey, a high-strength dairy effluent. The reactor demonstrated effective and stable biomethanation of whey in continuous mode without pH control. The chemical oxygen demand (COD) removal remained at around 80%, with the reactor pH being maintained neutral without buffering, in the organic loading rate (OLR) range of 0.8–2.4 g COD/l∙d. Although the COD removal decreased down to below 60% at higher OLRs along with acid accumulation, the methane production rate continued to increase with increasing OLR. On the other hand, the methane yield was maintained at 0.28–0.34 l/g COD throughout the experiment. The substrate removal and methane production kinetics were successfully described by the modified Stover–Kincannon model. The overall results suggest that BFS grains could be used as economic filter media for anaerobic treatment of cheese whey and other easily acidifying waste streams.

Tratamento das águas do processamento dos frutos do cafeeiro em filtro anaeróbio seguido por sistema alagado construído: I - remoção de matéria orgânica

Seis sistemas de tratamento, compostos por três filtros anaeróbios com escoamento descendente, seguidos por seis Sistemas Alagados Construídos (SACs), tiveram suas condições operacionais avaliadas quando utilizados no tratamento da água residuária do processamento dos frutos do cafeeiro (ARC). Os filtros foram confeccionados em PVC (1,5 m de altura e 0,35 m de diâmetro) e preenchidos com brita nº 2. Os SACs foram constituídos por caixas de madeira (1,5 m de comprimento, 0,4 m de altura e 0,5 m de largura), sendo impermeabilizados e preenchidos com brita "zero". A ARC teve o pH corrigido com cal até valores próximos a 7,0, e a concentração de nutrientes alterada, de forma a se obter uma relação DBO/N/P de 100/5/1. Em metade dos SACs foi plantado o azevém (Lolium multiflorum Lam.), e na outra metade, aveia-preta (Avena strigosa Schreb). Como resultado, observou-se que as espécies vegetais cultivadas nos SACs não influenciaram nas eficiências globais de remoção de poluentes pelos sistemas. Os sistemas que receberam as menores cargas orgânicas apresentaram as maiores eficiências de remoção de matéria orgânica, alcançando 78% para DQO e 70% para DBO. A remoção de SST foi superior a 70% em todos os sistemas avaliados, indicando a viabilidade da aplicação de filtro anaeróbio seguido por SACs no tratamento da ARC.

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.

SE—Structures and Environment: A Dual-reactor Anaerobic System for Complete Treatment of a Food Processing Waste

Anaerobic technologies are commonly employed for the initial treatment of food processing wastewater; however, they are not typically considered capable of treating wastewater to meet final discharge requirements. To assess the potential of anaerobic technologies to meet discharge requirements, the performance of two dual-reactor high-rate anaerobic systems fed with confectionery wastewater was investigated. The primary reactors in the system were operated at constant hydraulic retention times of 1·6 d. The secondary reactors were operated with hydraulic retention times of 0·8, 1·6, and 3·2 d. The secondary reactors, which were both downflow anaerobic filters, achieved maximum chemical oxygen demand (COD) removal rates when operated at a hydraulic retention time of 1·6 d. The brick-filled downflow anaerobic filter and the plastic-ring-filled downflow anaerobic filter produced average effluent five-day biochemical oxygen demand concentrations of 26 mgl−1 (COD=80 mg l−1) and 36 mg l−(COD=112 mg l−1), respectively. To examine the enhanced stability provided by the sequential reactor approach, the dual-reactor system was overloaded at 3·5 times the normal COD concentration (8000 mg l−1) for an 8 h period. The secondary reactors were able to accommodate the increased organic loading emitted from the primary reactors, maintaining an overall removal efficiency of >994%. The results suggest that full anaerobic treatment of readily degradable food waste streams may be realistic, and that a sequential reactor approach significantly enhances overall process stability.

ENHANCING DAIRY LAGOON PERFORMANCE WITH HIGH–RATE ANAEROBIC DIGESTERS

In a twostage study, the possibility of using highrate anaerobic digesters to enhance the performance of dairylagoons was explored. Four anaerobic sequencing batch reactors (ASBR) and four downflow anaerobic filters (DFAF) weretested, with two of each type operated at 25
C, and the other two at 35
C. The first stage of the experiment explored usingthe highrate digesters on liquid effluent from a screwpress treating dairy manure slurry. The firststage experimentdemonstrated that settling processes, rather than biodegradation, accounted for most of the organic matter reduction in bothreactor types, when operated at a 0.5d hydraulic retention time. Specifically, settling accounted for an average of 100% ofthe chemical oxygen demand (COD) removal in the ASBR reactors, and for an average of 72% of the COD removal in theDFAF reactors. These results prompted the second stage of the experiment, which explored the possibility of using the reactorsto remove volatile fatty acids (VFAs) from dairy lagoon supernatant. Diluted manure slurry was spiked with acetic acid (HAc)to simulate the supernatant of an overloaded lagoon. At VFA loading rates of 1.0 and 3.0 kg HAc m 3 d 1 , both reactor typesachieved moderate VFA removal. However, at a loading rate of 6.0 kg HAc m 3 d 1 , the ASBR reactors were ineffective,whereas the DFAF reactors, at both 25
C and 35
C, removed more than 80% of the influent HAc. At a loading rate of 12 kgHAc m 3 d 1 , the DFAFs achieved removal rates of 75%; removal rates dropped to 50% at the maximum loading tested, 24 kgHAc m 3 d 1 . Based on these experiments, it appears that the DFAF reactors are suited to the task of rapidly removingaccumulated VFA from lagoon supernatant.

Sequential Two-stage Anaerobic Treatment of Confectionery Wastewater

A bench-scale, two-reactor sequential anaerobic treatment system was tested for its ability to remove organic carbon from confectionery wastewater. The system consisted of an upflow anaerobic sludge blanket operated at 35°C followed by a downflow anaerobic filter operated at ambient temperature (∼ 25°C). The system had a total hydraulic retention time of 2·4 d. Reactor performance was characterized by monitoring chemical oxygen demand (COD), pH, volatile fatty acid concentration, alkalinity and biogas production and composition.An overall COD treatment efficiency of 98% was observed for the system, at an overall organic loading rate of 12·5 kg/m3/d (as COD). The upflow anaerobic sludge blanket worked extremely well at high organic loadings (COD added at 20 kg/m3/d). Effluent recycle enabled the upflow anaerobic sludge blanket to operate with influent COD concentrations up to 30 g/l. The downflow anaerobic filter maintained effluent COD concentrations below 400 mg/l, and effectively buffered fluctuations in the effluent of the upflow anaerobic sludge blanket reactor.

Treatment of settled cattle-wastewaters by downflow anaerobic filter

Abstract Screened and settled cattle waste was treated in a downflow anaerobic filter filled with ceramic raschig rings. The influent had a TS concentration of 16014–17556 mg/litre and was applied at retention times from 0·5 to 4 days. The removal ranged from 55 to 87% in soluble COD and from 72 to 90% in soluble BOD. The biogas productivity ranged from 0·8 to 4·5 V/VR day while the methane productivity was 0·7-2·8 V/VR day. In spite of the high concentration of suspended solids in the influent, clogging of the reactor was not observed during the experiments, which lasted about a year.

Torula yeast wastewater treatment by downflow anaerobic filters

The by-products, molasses, of the sugar industry are used as a source of biomass. Torula yeast is obtained from molasses fermentation and used as animal food. After the separation of the yeast, a highly concentrated wastewater is produced. At present, the wastewater is spread on the land or discharged to streams, causing serious pollution problems. More than 30 000 m3 of wastewater from the torula yeast industry are daily produced with an average COD concentration of 20 g/litre and a pH around 4·5 (Travieso et al., 1988, Report to Sugar Industry Ministry, Havana, Cuba). Considering the advantages of the anaerobic downflow filter for the treatment of acidic wastewaters a study of this system for the treatment of torula yeast wastewaters was developed. The effects of the support media, the hydraulic retention time, the organic loading and the effluent recirculation on the filter efficiency were studied. Among gravel media, polystyrene media and ceramic media, it was demonstrated that ceramic media were the most effective. For the operational parameters studied, a hydraulic retention time of 3 days, organic volumetric loading of 6 kg COD/m3 day and the use of an effluent recirculation ratio of 1:1 were considered the optimum.

Discussion Report on Reactor Design of Anaerobic Filters and Sludge Bed Reactors

The discussion report of the session dedicated to reactor design is focused on sludge bed reactors and on upflow and downflow anaerobic filters. The reactor hydrodynamics and their relationship with process efficiency and stability are particularly discussed. The discussion ends with the formulation of some suggestions of design parameters for project engineers.

A note on anaerobic treatment of currant-finishing wastewater in downflow anaerobic filters and the effect of media design on their performance

Two downflow anaerobic filters with different plastic media of the same specific surface area, treating currant-finishing wastewater are described. COD removal for modular plastic media with a cross-flow design was 80% and 75% for loadings of 8 and 10 kg COD/m 3 day respectively. COD removal for pall-rings media gradually decreased from 90% to 57% as loadings gradually increased from 0·6 to 6 kg/m 3 day. The downflow anaerobic filters have a low performance compared with other high-rate anaerobic reactors, the UAF, UASB and AFB.

Treatment of Landfill Leachate by an Anaerobic Filter Part 2: Pilot Studies

Abstract A 4-month study of pilot-scale anaerobic filters was conducted on the treatment of leachate generated from the Beare Road Landfill site in Metropolitan Toronto. The study examined filter performance in both upflow and downflow modes of operation using two types of support media, via plastic biorings and granite stones. No significant difference in removal efficiences, quantity of gas produced and its methane content, was found between upflow and downflow anaerobic filters nor between the plastic biorings and the granite stone media. An efficiency of 66-72% COD removal was achieved at a hydraulic detention time as low as 12 hours. The total gas production ranged between 400-500 L/kg COD destroyed. Methane content in the gas remained between 80-84%.