Showing papers on "Hydraulic retention time published in 1987"

Improved Sludge Gasification by Two‐Phase Anaerobic Digestion

Abstract: The objectives of this research are to study the relative efficacies of two‐phase and single‐stage, high‐rate anaerobic sludge digestion at mesophilic and thermophilic temperatures at several levels of hydraulic residence time (HRT), organic loading rate, and feed consistency. In addition, the effects of pH, temperature, and HRT on acid‐phase digestion are studied. Data from continuous‐flow digestion studies showed that the two‐phase process is better than single‐stage digestion under all test conditions when compared on the bases of gas yield and production rate, reductions of volatile solids, carbohydratelipid‐protein conversions, buffer‐capacity, and unconverted volatile acids in the effluent. A mesophilic two‐phase system exhibits about the same methane yield and solids reduction at a 3‐day HRT as those of single‐stage high‐rate digestion at 15‐ and 17‐day HRT's. The enhanced stability of two‐phase digestion relative to single‐stage digestion increases as the system loading and hydraulic dilution rate...

Biooxidation of coal gasification wastewaters using fluidized-bed bioreactors

Abstract: Process condensate wastewaters from two fixed-bed gasifiers have been treated successfully using a laboratory-scale, fixed-film, fluidized-bed bioreactor. Both dilute (1 to 2% raw wastewater) and more concentrated (50% stripped wastewater) were treated continuously for periods of one to three months. Biological activity was stable, recovery from upsets was rapid, and reaction rates were high due to the high concentration of microorganisms retained on the support particles. Removal of phenolics exceeded 99%, and removal of chemical oxygen demand was typically 75 to 85% for the 50% stripped wastewater with a hydraulic residence time in the bed of ˜5 to 7 h. Sludge production rates were comparable to rates in suspended growth systems.

Treatment of a landfill leachate in powdered activated carbon enhanced sequencing batch bioreactors

Abstract: Addition of powdered activated carbon (PAC) significantly improved treatment of a chemical waste landfill leachate in sequencing batch bioreactors (SBRs). Concentrations for many of the monitored halogenated organic compounds in the effluent were below their respective detection limits. Excellent treatment efficiency was achieved under a variety of operating conditions: wastewater composition, feed rate, hydraulic retention time, organic loading, PAC dosages, biomass and PAC concentrations in the bioreactors. The PAC-SBR performance was unaffected when wastewater feeding was suspended during weekends and holidays. The PAC-SBR treatment cost is much lower than either that of the conventional granular activated carbon adsorption technology or the two-stage process of biodegradation and carbon treatment.

Nitrification process in waste water treatment

Abstract: The ammonia concentration present in waste water is reduced by treating the waste water with a suspended growth microbial system such as an activated sludge containing organisms of the genus Nitrosomonas and organisms of the genus Nitrobacter, but in which the microbial activity of Nitrobacter is effectively inhibited. The process includes a step of treating the microbial system under conditions effecting inhibition of the Nitrobacter but substantially unaffecting the growth and metabolic characteristics of the Nitrosomonas, and subjecting the ammonia containing waste water to the so treated microbial system for a hydraulic retention time which is less than the recovery time of the inhibited Nitrobacter. As a result, the retrograde step of nitrite-nitrate conversion in the overall denitrification process also is reduced or eliminated, with consequent energy and cost savings.

Factors affecting biological phosphorus removal for the vip process, a high-rate university of capetown type process

Abstract: The phosphorus removal capabilities of the Virginia Initiative Plant (VIP) process, a high-rate biological nutrient removal (BNR) process, are presented and compared to the high-rate A2/0 and the low-rate University of Capetown (UCT) processes. The results indicate superior phosphorus removal capability for the VIP process compared to the A2/0 and UCT processes. In general, VIP process phosphorus removal was maximized by operation at the lowest possible total process mean cell residence time (MCRT) and with an aerobic hydraulic residence time (HRT) not exceeding 4 hours. A total process MCRT of 5 days provided acceptable nitrogen removal and excellent phosphorus removal for wastewater temperatures of 20°C or above, while a total process MCRT of 20 days would be required at a temperature of 12°C. Operation of the VIP process at an aerobic HRT greater than 4 hours apparently resulted in oxidation of stored organic matter that adversely affected phosphorus uptake kinetics. Data analysis suggested that the VIP process could have been operated at an anaerobic HRT as short as 20 minutes. Superior phosphorus removal performance was observed for the VIP process compared to the A2/0 process when the BOD5/TPO4 ratio of the wastewater was significantly less than 20.

The effects of environmental factors on acid-phase digestion of sewage sludge

Abstract: The two-phase anaerobic digestion process consists of two fermenters operated in series, wherein the acidification and gasification reactions are optimized in separate reactors to improve the overall system conversion efficiency. This paper discusses the results of tests conducted with bench-scale complete-mix acid-phase digesters to determine the effects of culture pH, temperature, and hydraulic retention time (HRT) on the efficiency of sewage sludge digestion. Tests were conducted at culture pH's of 5, 5.5, 6, and 7 at mesophilic (35/degree/C) and thermophilic (55/degree/C) temperatures and at HRT's of 1.3 and 2 days. Digestion efficiencies were determined on the basis of volatile acid production, gas production, and the reduction of the major particulate components of the feed sludge (crude protein, carbohydrates, and lipids). Efficiencies were highly dependent on each of the three control factors and were generally optimized at the higher extremes of pH, temperature, and HRT tested. 9 refs., 2 figs., 10 tabs.

Relationship between the concentration of acetate in the feed and the composition of a biofilm in an anaerobic filter

Abstract: Different methanogenic associations developed in two anaerobic filters operated with a very short hydraulic retention time and fed with different concentrations of acetate. An organic load of 30 g of CH3COO .1‐1.d‐1 was reached with only Methanosarcina sp. and hydrogenophilic bacteria in the reactor fed with a high concentration of acetate. Methanothrix sp. only developed in the reactor fed with the low concentration of acetate. The composition of the biofilm given in proteins and polysaccharides, depended on the concentration of the carbon source.

Application de lit fluidise anaerobie au traitement des effluents a forte charge organique

Abstract: This paper presents the evaluation of an anaerobic fluidized bed reactor for the treatment of effluent of a tapioca plant. The volume of the reactor was about 40 liters; actived carbon was used as support of bacteria. The influent had 6,4 kg m‐3 COD and contained 4,4 kg m‐3 suspended solids (SS). The hydraulic retention time varied from 5 to 29 hours. The values of efficiency varied from 57.9 to 88.3 % COD for an average yield of biogaz of 2.2 to 6.5, i.e. in the range of 0.355 to 0.54 m3 biogaz kg‐1 COD.

Reticulated foam as a biomass support medium in the anaerobic digestion of an industrial wastewater.

Abstract: This work reports the pilot-scale investigation of various anaerobic reactor systems treating a fruit washing wastewater An open cell reticulated foam was used as a biomass support media (BSM) The foam pads (25 mm cubes) were randomly packed in the 25 m- 3 reactor with an unpacked section beneath the bed Four general operational regimes were evaluated These were: single and two stage operation, with and without effluent recycle Performance was monitored throughout each run in terms of maximum COD loading rate and minimum attainable hydraulic retention time Biomass concentrations, both within the media and freely suspended between the biomass support particles were measured on samples from each operating regime, their acetoclastic activity being determined in a laboratory test A method was developed to ascertain whether a difference in biomass activity existed between the outside of an individual biomass support particle and at the centre of the particle, using a radioactively labelled substrate It was concluded that a two stage system without recycle provided the best performance with respect to the the maximum attainable loading rate (116 kgCODm- 3 day) This was approximately twice that for any of the other systems tested The minimum hydraulic retention time corresponding to this loading was approximately 10 d The superior performance of the two stage system without recycle was attributed to the increased acetoclastic populations brought about by the pre-acidified feed and the plug flow removal kinetics exhibited in reactors without recycle Two stage systems produced higher levels of biomass in the reactor than their single stage counterparts and a large proportion of the total biomass inventory was present as suspended growth in systems without recycle Tracer studies showed that the actual HRT was much less than that calculated from flow rate and reactor volume, indicating that large areas of the reactor were not accessible to the substrate Experiments investigating activity gradients in the BSM indicated that a significant difference existed between the acetoclastic activity of biomass at the centre of a colonized particle and that on the surface It may be concluded that substrate diffusional limitations played an important role in determining the performance of this type of biomass support Electron microscope examination of BSP fragments gave little information other than the existence of both attached and suspended growth Most of the bio mass was present as a dense fibrillar network

Experience with Full-Scale Biopaq — U.A.S.B.—Plants Treating Various Types of Effluent

Abstract: For the past several decades, wastewater treatment in het industrial countries has been dominated by aerobic processes using bacteria that require oxygen to metabolize dissolved organic compounds and convert them into carbon dioxide and settleable solids.