Showing papers on "Hydraulic retention time published in 1984"

Start-up of anaerobic filters containing different support materials using pig slurry supernatant

Abstract: Start-up of four laboratory-scale anaerobic filters, containing clay, coral, mussel shell and plastic pall ring support materials, was achieved at a hydraulic retention time of 6 days and a constant COD loading, ab initio, of 5 kg COD.m−3.d−1 using a pig slurry supernatant feed. Start-up was most rapid with the clay filter (c. 20 days) and was slowest with the filter containing the mussel shell support. Irrespective of the time taken for start-up, the performance of all four filters at steady-state was similar, with COD removal efficiencies of 69–73% being attained. Start-up and steady-state performance did not correlate directly with either the unit surface area or the porosity of the support materials utilised.

Control of Activated Sludge Bulking

Abstract: The settling properties of the activated sludge cultivated in both single and multiple compartment systems were thoroughly investigated under various BOD/N ratios in the wastewater and at a hydraulic retention time of 24 hrs. The present study found that the compartmentalized system could not only achieve a better effluent quality but also produce a higher sludge settleability if the BOD/N ratio was not in excess of 130:1. The performance of the compartmentalized system highly depended upon the physical arrangement of the reactor compartments or the value of the dispersion number, that is, the higher the compartment number or the lower the dispersion number, the higher the percentage organic substrate removal. This result was mainly due to the fact that both the sludge settling and the substrate utilization rates were higher when the mixed activated sludge culture was cultivated in the compartmentalized system with low dispersion number. The major filamentous micro-organisms which were observed in the conventional single-stage reactor system were: Sphaerotilus sp. form I (\IS. natans\N), and form II, Type 0961, Type 021N, Type 0581 and Type 0803. These causative filamentous micro-organisms could exist even when the activated sludge system was operated under the DO sufficient condition.

Anaerobic digestion of solid fruit waste supplemented with poultry manure in a horizontal plug‐flow reactor

Abstract: Anaerobic digestion of apple press cake in a horizontal plug‐flow reactor (hydraulic residence time 40 d: 2.20 kg organic solids/m3.d) resulted in 78.1% conversion of organic solids and a gas yield of 0.510 m3/kg organic matter digested. Poultry manure fed weekly (4 kg total solids/m3) as the sole source of supplementation maintained levels of 400 mg ammonia nitrogen/1 and 13 mg phosphorus/1, and also maintained satisfactory levels of alkalinity and pH.

Growth response of a nitrogen fixer (anabaena flos-aquae, cyanophyceae) to low nitrate1

Abstract: Anabaena flos-aquae (Lyngb.) Breb. was grown in varying concentrations of nitrate. Specific growth rates, as estimated in batch culture, were constant and approached the maximum rate at all concentrations of NO3−-N tested bewteen 0 and 400 μ/L. Steady-state biomass, as determined in semicontinuous culture, did not vary with NO3− at slower dilution rates. However at a faster dilution rate, significantly less biomass occurred in intermediate concentrations of NO3− than in either higher or lower concentrations. The results indicate that both growth rate and standing crop are maximized by either N2 fixation or NO3− assimilation, but extracellular NO3− reduces the rate of N2 fixation. Consequently, at very low NO3− concentrations, growth is virtually maximized by N2 fixation alone, and at high concentrations of NO3−, N2 fixation is inhibited but growth is maximized by assimilation of NO3−. At intermediate concentrations of NO3−, growth becomes a function of NO3− assimilation augmented by N2 fixation. In this case, full growth potential is realized only if hydraulic residence time is sufficiently long to compensate for the reduced rate of N2 fixation. Growth rate and standing crop are not diminished in response to the large amount of energy allocated to N2 fixation. Instead, other cellular processes are probably affected negatively during N2 fixation.

Nitrification of anaerobically treated coal gasifier effluent

Abstract: Coal gasifier effluent with high phenol, cresols and ammonia concentrations and lower amounts of cyanide, thiocyanate and other organic compounds was nitrified after treatment in an anaerobic fluidised-bed granular activated carbon filter. The single-stage biological nitrification system was operated at a solids retention time of 31 days and a hydraulic retention time of 18-30 hours. Removal efficiencies were 97% for total Kjeldahl nitrogen, 91% for TOC and 85% for COD; residual phenol and o-cresol were completely removed and removal of residual m-cresol and p-cresol depended on concentration. The nitrification process was inhibited by more than 15 mg/l of m-cresol and p-cresol, but this could be eliminated by addition of powdered activated carbon or periodic replacement of a portion of the granular activated carbon in the anaerobic filter.

Considerations in design and operation of a biogas plant.

Abstract: The operation of a novel anaerobic digester using cow dung as substrate is described and preliminary results presented. The digester is designed to maximise both solids retention and the gentle stirring energy released by evolved gases; the resultant configuration of the digester has the form of a tower. Laboratory scale studies using grass cuttings gave a yield of 1.9 digester volumes of gas (70% methane) per day at low hydraulic retention time (10 days) and a solids loading of 7% TS. An 8000 1 digester gave a consistently high methane content (greater than 70%) of biogas from a cow slurry substrate.

Energy recovery from agroindustrial wastes with prevalently solute pollutants using fixed-bed anaerobic reactors

Abstract: A process for anaerobic digestion of agroindustrial wastes containing mainly soluble pollutants was developed utilizing fixed-bed reactors. A pilot plant at a sugar refinery with two reactors in parallel, respectively of 10 and 50 m/sup 3/ operating volume, has functioned successfully in treating wastes produced in regenerating ion-exchange columns used to purify the sugar juices. With an hydraulic retention time (HRT) of less than one day, a maximum gas production of 11.5 volumes per operating volume of reactor per day was obtained together with a reduction of up to 80% of the biological oxygen demand for five days (BOD5), and volatile solids and up to 70% of the chemical oxygen demand (COD). The gas contained from 70 to 75% methane. On the basis of these results, a full-scale industrial plant was built which produced up to 7500 m/sup 3/ a day of biogas. The process has been found suitable for a large number of industrial wastes, especially when plants are seasonally operated.

Mesophilic anaerobic digestion of screened dairy manure using conventional and fixed-film reactors.

Abstract: 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 4L anaerobic reactors (conventional and fixed-film) receiving screened dairy manure and operated at 35°C was compared. Dairy manure filtrate with 4.4% TS and 3.4% VS (average value) was prepared from 1:1 manure/water slurry. The feed material was added itermittently at loading rates ranging from 2.34 to 25 and 2.25 to 778 g VS/L.d respectively for the conventional and fixed-film reactors. Maximum methane production rate (L.CH4/L.digester/day) for the conventional reactor was 0.63 L.CH4/L.d achieved at a 6 day hydraulic retention time (HRT). For the fixed-film reactor, the maximum production rate was 6.20 L.CH4/L.d when operated at a loading rate of 259 g.VS/L.d (3 hrs HRT). The fixed-film reactor was capable of sustaining a loading of 778 g.VS/L.d (1 hr. HRT). The fixed-film reactor performed much better than the conventional reactors. The average biogas methane content from the fixed-film reactor (65.8%) was always higher than from the conventional reactors (61.6%). These results indicate that a large reduction of required reactor volume is possible through application of a fixed-film concept.

Process for the biological decomposition of organic impurities in highly concentrated waste waters by means of suspended bacteria.

Abstract: The process is characterised in that the decomposition is carried out at a constant redox potential (E) in the range from -200 to -350 mV, at a constant pH between 7.0 and 9.0 and with an approximately constant hydraulic retention time. More than 90 % decomposition is achieved.