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

Evaluation of a zeolite/anaerobic buffled reactor hybrid system for treatment of low bio-degradable effluents

The main objective of this work was to reduce the inhibitory effects of high contents of organics, ammonia, and heavy metals in an anaerobic buffled reactor (ABR), and to prevent the sludge wash-out using zeolites as media. In this work, a pilot scale of ABR with 8 compartments and a working volume of 14.4 L was used, and the last four ABR compartments were filled with a zeolite. The bioreactor was operated at HRTs of 3, 4, and 5 days, zeolite filling ratios of 10, 20, and 30%, and influent chemical oxygen demand (COD) concentrations of 10,000, 20,000, and 30,000 mg/L. The results obtained showed that the maximum removal efficiencies of COD and BOD₅ reached 78 and 68%, respectively. The maximum removal was observed at a HRT of 5 days, a 30% medium filling ratio, and a COD of 10,000 mg/L. Increasing the filling ratio in the reactor increased the removal efficiencies of COD and BOD₅ but increasing the concentration of the influent COD and decreasing HRT reduced the removal efficiency of the reactor. The initial BOD₅/COD ratio was equal to 0.36, which increased by 46% when the medium filling ratio was elevated to 30%. The maximum biogas yield was 0.23 L/g of COD_Removed, and the specific methanogenic activity test verified the toxicity effect of the leachate on the gas-producer organisms. The results of scanning electronic microscopy and EDS showed that the zeolite medium immobilized the microorganisms and a biofilm was formed. Also the zeolite, as a well-known ion exchanger, decreased the concentrations of the major inhibitors (ammonia and heavy metals) and improved the reactor efficiency.

Effects and optimization of the use of biochar in anaerobic digestion of food wastes

The addition of various amounts of biochar to anaerobic digestion of food wastes at different ratios of inoculum to substrate (ISR) was investigated to evaluate the effect of biochar as a functional additive and to optimize the additive dosage of biochar. The biochar treatments at ISR 2, 1, and 0.8 shortened the lag phase of digestion by -20.0%-10.9%, 43.3%-54.4%, and 36.3%-54.0%, and raised the maximum methane production rate by 100%-275%, 100%-133.3%, and 33.3%-100%, respectively, compared to control without biochar. Biochar also enhanced the degradation rate of dissolved organics and volatile fatty acids. Furthermore, the amount of biochar with best effectiveness at ISR = 2, 1, and 0.8 was 2.5, 0.625, and 0.5 g g(-1)-waste, respectively. Therefore, the effectiveness of biochar depended on the additive amount of biochar and at the same time the inoculum amount, implying a complementary role of abiotic biochar to biotic inoculum.

Microbial anaerobic digestion (bio-digesters) as an approach to the decontamination of animal wastes in pollution control and the generation of renewable energy

With an ever increasing population rate; a vast array of biomass wastes rich in organic and inorganic nutrients as well as pathogenic microorganisms will result from the diversified human, industrial and agricultural activities. Anaerobic digestion is applauded as one of the best ways to properly handle and manage these wastes. Animal wastes have been recognized as suitable substrates for anaerobic digestion process, a natural biological process in which complex organic materials are broken down into simpler molecules in the absence of oxygen by the concerted activities of four sets of metabolically linked microorganisms. This process occurs in an airtight chamber (biodigester) via four stages represented by hydrolytic, acidogenic, acetogenic and methanogenic microorganisms. The microbial population and structure can be identified by the combined use of culture-based, microscopic and molecular techniques. Overall, the process is affected by bio-digester design, operational factors and manure characteristics. The purpose of anaerobic digestion is the production of a renewable energy source (biogas) and an odor free nutrient-rich fertilizer. Conversely, if animal wastes are accidentally found in the environment, it can cause a drastic chain of environmental and public health complications.

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.

Combined processes of two-stage Fenton-biological anaerobic filter-biological aerated filter for advanced treatment of landfill leachate

There are numerous non-biodegradable organic materials in the mature landfill leachate. To meet the new discharge standard of China, additional advanced treatment is needed for the effluent from the biological treatment processes of leachate. In this study, a combined process including two stages of "Fenton-biological anaerobic filter (BANF)-biological aerated filter (BAF)" was evaluated to address the advanced treatment need. The Fenton oxidation was applied to reduce chemical oxygen demand (COD) and enhance biodegradability of refractory organics, and the BANF-BAF process was then applied to remove the total nitrogen (TN). The treatment achieved effluent concentrations of COD<70 mg/L, TN<40 mg/L and NH(3)-N<10 mg/L. The removal efficiency of COD and TN were 96.1% and 95.9%, respectively. The effluent quality met the new discharge standard for Pollution Control on the Landfill Site of Municipal Solid of PR China (GB16889-2008). The operation cost of these processes was about 36.1CHY/t (5.70USD/t).

Dynamic transition of microbial communities in response to acidification in fixed-bed anaerobic baffled reactors (FABR) of two different flow directions

Two five-compartment fixed-bed anaerobic baffled reactors (FABRs) were operated under deteriorative and stable conditions. The FABRs were identical except for flow direction: one was horizontal (H-reactor) and the other was vertical (V-reactor). The microbial community dynamics in 1, 3 and 5 compartments were analyzed using denaturing gradient gel electrophoresis (DGGE), 16S rRNA gene clone library screening and quantitative PCR. After start-up, the Methanomicrobiales were typically dominant in adhering sludge of 5th compartments of two reactors. Because methanogenesis mainly occurred in the latter compartment, Methanomicrobiales were likely to play important roles in FABRs. FABRs recovered from performance deterioration very quickly. Meanwhile, methanogens and dominant methanogens greatly increased in every compartment of two reactors. Our results indicated that 16S rRNA levels of methanogens in the adhering sludge were higher than those in the deposited sludge and the adhering fraction of V-reactor held up more acid-resistant bacteria and methanogens than that of H-reactor.

Bipolar effects of settling time on active biomass retention in anaerobic sequencing batch reactors digesting flushed dairy manure

Active biomass retention is a technical challenge in anaerobic digester treating dilute animal manure that contains solids particles. A strategy was tested using fibers in the dairy manure as biomass carriers by controlling settling time. Settling time ranging from 0.5 to 60min were applied to eight anaerobic sequencing batch reactors to investigate their effects on active biomass retention in anaerobic digestion of flushed dairy manure. Results revealed that there existed a critical settling time at 2min at which only minimum amount of active biomass was retained, and as settling time increased or decreased from this threshold, more active biomass could be retained. Gravity settling and selection pressure theories were suggested to account for the results. A model integrating these two effects was developed and verified with the experimental data. Knowledge derived from this study may lead to innovative bacterial retention technology for cost-effective anaerobic digestion of dairy wastes.

The performance of biological anaerobic filters packed with sludge-fly ash ceramic particles (SFCP) and commercial ceramic particles (CCP) during the restart period: effect of the C/N ratios and filter media

Two lab-scale upflow biological anaerobic filters (BAF) packed with sludge-fly ash ceramic particles (SFCP) and commercial ceramic particles (CCP) were employed to investigate effects of the C/N ratios and filter media on the BAF performance during the restart period. The results indicated that BAF could be restarted normally after one-month cease. The C/N ratio of 4.0 was the thresholds of nitrate removal and nitrite accumulation. TN removal and phosphate uptake reached the maximum value at the same C/N ratio of 5.5. Ammonia formation was also found and excreted a negative influence on TN removal, especially when higher C/N ratios were applied. Nutrients were mainly degraded within the height of 25 cm from the bottom. In addition, SFCP, as novel filter media manufactured by wastes-dewatered sludge and fly ash, represented a better potential in inhibiting nitrite accumulation, TN removal and phosphate uptake due to their special characteristics in comparison with CCP.

Anaerobic treatment of synthetic medium-strength wastewater using a multistage biofilm reactor

A laboratory-scale multistage anaerobic biofilm reactor of three compartments with a working volume of 54-L was used for treating a synthetic medium-strength wastewater containing molasses as a carbon source at different influent conditions. The start-up period, stability and performance of this reactor were assessed at mesophilic temperature (35 degrees C). During the start-up period, pH fluctuations were observed because there was no microbial selection or zoning, but as the experiment progressed, results showed that phase separation had occurred inside the reactor. COD removal percentages of 91.6, 91.6, 90.0 and 88.3 were achieved at organic loading rates of 3.0, 4.5, 6.75 and 9.0 kg COD/m(3) day, respectively. A decrease in HRT from 24 to 16 h had no effect on COD removal efficiency. When HRT decreased to 8h, COD removal efficiency was still 84.9%. Recirculation ratios of 0.5 and 1.0 had no effect on COD removal but other factors such as the volatile fatty acid (VFA) content were affected. The effect of toxic shock was also investigated and results showed that the main advantage of using this bioreactor lies in its compartmentalized structure.