ISSN:1061-4303    

DOI:10.1002/j.1554-7531.1996.tb00172.x

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

Pilot scale experiments have been conducted to investigate the use of aerobic thermophilic pretreatment (ATP) of mixed (waste activated and primary) sludge before mesophilic anaerobic digestion to meet Class A sludge pathogen control requirements. The ability of ATP to controlNocardiapresent in the waste activated sludge, and hence prevent foaming in the subsequent anaerobic digestion, was also investigated. Aerobic thermophilic pretreatment of mixed sludge before anaerobic digestion was able to produce sludge that can meet the following Class A pathogen reduction requirements: fecal coliform density<1 000 MPN/g total solids orSalmonellasp. density<3 MPN/4 g total solids; time and temperature requirements (1.8 hr at 63°C); enteric virus density38% volatile solids reduction). ATP was able to controlNocardiato below detectable levels, whereas theNocardialevels in the control anaerobic digester were ≥105intersections/g VSS when both were fed mixed sludge containingNocardiafilament counts in excess of 105intersections/g VSS. The ATP system was also able to produce higher volatile solids (VS) reduction, higher methane content in sludge gas, and lower sludge supernatant COD when compared with those achieved in the control anaerobic digester.

ISSN:1061-4303    

DOI:10.2175/106143096X128117

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

Batch reactors and serum bottles were used to determine kinetics of growth, substrate utilization, and sulfide inhibition [dissolved sulfide (DS) and hydrogen sulfide (H2S)] in anaerobic systems fed propionate and sulfate. Thermodynamic analyses indicated six major groups of organisms were active in such systems: incomplete propionate oxidation by sulfate‐reducing bacteria (SRB), propionate fermentation to acetate and hydrogen, acetate‐oxidizing SRB, aceticlastic methanogenesis, hydrogenotrophic SRB, and hydrogenotrophic methanogens. Kinetic parameters determined for each of these groups were bacterial yield, decay coefficient, maximum specific substrate utilization coefficient, half‐velocity constant, and inhibition coefficient (uncompetitive). Results indicated that the kinetic and thermodynamic advantages of acetate‐utilizing SRB were erased by their sensitivity to sulfide toxicity. In addition, propionate fermenters were also very sensitive to sulfide toxicity. These results help to explain why methanogenesis from complex substrates occurs even in the presence of high concentrations of DS and H2S.

ISSN:1061-4303    

DOI:10.2175/106143096X128126

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

The effects of substrate and pH on biofilm nitrification were studied using a microelectrode technique and a microslicing technique. Three different kinds of biofilms were cultured using lab‐scale, rotating drum biofilm reactors fed with synthetic wastewaters. The measured concentration profiles provide direct experimental evidence of the substrate and pH effects on biofilm nitrification. It was found that pH decreases within the nitrifying biofilm depended on the mole ratio of HCO−3/O2. When this mole ratio was>5, the maximum pH decrease within the nitrifying biofilm was<0.4–0.6 pH units. When this ratio was2–2.5) was observed during the study. It was found that increases in glucose loading or ammonium loading caused more consumption of oxygen, which resulted in inhibition of the biofilm nitrification. The bacterial trophic population measurement revealed that even in a pure nitrification system, heterotrophs could exist in the nitrifying biofilm. In biofilms cultured with an influent COD of 170 mg/L or higher, the numbers of nitrifiers were always four to five orders lower than those of heterotrophs. This study demonstrates that competition between heterotrophs and nitrifiers for substrate (including O2) and space greatly affects the degree of pH decreases within nitrifying biofilms.

ISSN:1061-4303    

DOI:10.2175/106143096X128504

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

Pools of mobile dense nonaqueous phase liquids (DNAPL) are often found perched above capillary boundaries at sites where DNAPLs have been managed. An approach to partially address risks posed by pools of mobile DNAPLs is to recover the mobile fraction of the DNAPL and, thereby, limit the potential for future DNAPL migration.
During the last 8 yrs, development and implementation of an effective mobile DNAPL recovery technique has been ongoing at a former wood‐treating plant located in Laramie, Wy. The technology relies on dual horizontal water and DNAPL recovery drainlines, installed in a single trench, coupled with parallel single water delivery drainlines. By cycling water between the upper recovery and parallel delivery drainlines, DNAPL is hydraulically driven to the lower recovery drainlines.
Presently, full‐scale DNAPL recovery operations at the site are in their fourth year of an approximate 8‐yr program. An area of ∼24 ha is being addressed. To date, ∼4.9 million L of DNAPL has been recovered and an endpoint of 95% recovery of mobile DNAPL is being achieved. Review of this technology's development and implementation provides insight into a unique approach to mobile DNAPL recovery which is likely applicable at other sites.

ISSN:1061-4303    

DOI:10.2175/106143096X128513

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

Discarded solid material derived from or soiled with fecal matter is commonly disposed in sanitary landfills. This material includes wastewater solids, pet feces, infectious wastes, and soiled disposable diapers. Such materials may contain indicator organisms, as well as human pathogens, including viruses. The aim of the present work was to analyze the health risk to humans from ingesting untreated groundwater obtained from aquifers subject to contamination from landfills receiving such materials. Uncertainty and variability associated with source composition as well as transport processes were included. It was concluded that, even with conservative assumptions, the health risk to humans from exposure to microbial pathogens of fecal origin deposited in well–designed and operated sanitary landfills is below levels currently considered to be acceptable under U.S. drinking water regulations applicable to treated potable water supplies.

ISSN:1061-4303    

DOI:10.2175/106143096X128522

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

The stripping of volatile organic compounds (VOCs) by surface aerators was evaluated in experiments performed at field scale. Each experiment consisted of dosing a tank containing tapwater with a selection of VOCs, activation of the aerator, and subsequent monitoring of the disappearance of the compounds. The tank contents were deoxygenated before the experiment thereby allowing concurrent measurement of the uptake of oxygen. Experiments were performed with two aerators with differing power inputs and aeration patterns and over a range of temperatures from 3 to 22°C. Overall mass transfer coefficients were calculated for each compound in each experiment. The impacts of temperature and aerator horsepower on the mass transfer coefficients of the candidate compounds were examined and relationships were calibrated with the experimental data. The fundamental gas and liquid mass transfer coefficients were calibrated and the ratio of gas to liquid phase mass transfer coefficient was estimated to range from 16 to 24. The estimated ratio ofkg/klwas found to be relatively insensitive to variations in the Henry's Law coefficient over the range typically observed in the literature. The observed ratio was lower than that previously reported in the literature and would suggest a greater impact of gas phase resistance than previously thought. The lower value of the ratio may be attributed to mass transfer limitations caused by entrained air.

ISSN:1061-4303    

DOI:10.2175/106143096X128531

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

Microbial granulation was examined in four lab‐scale upflow anaerobic sludge blanket (UASB) reactors at 35°C. The reactors had working volumes of 3.2, 5.0, 7.6, and 9.4 L. A synthetic wastewater of glucose, peptone, and meat extract was used as substrate and anaerobic digested sludge as seed. The reactors were fed 1 000, 2 000, 5 000, and 10 000 mg COD/L. The start‐up was followed by maintaining a high microbial load index (the ratio of sludge loading rate applied to specific methanogenic activity measured) of ∼0.8 in each reactor. Microbial granulation was initiated within 1 month and matured within 4 mo despite different influent substrate concentrations. The granulation process was characterized by acclimation, granulation, and maturation. However, the growth rates and the granules cultivated differed significantly. LargeMethanothrix‐like species (thrix granules) were cultivated with 1 000 to 5 000 mg COD/L influents, and smallMethanosarcinalike species (sarcina granules) were cultivated with 10 000 mg COD/L influent. The thrix granules with median diameters of 2.5–3.4 mm exhibited better settleability, higher substrate affinity, and slightly higher bioactivity than the 0.54‐mm sarcina granules. With thrix granules, the reactors operated efficiently and stably at a volumetric loading rate (VLR) of 30–40 g COD/L · d and/or a hydraulic retention time (HRT) of 1–2 h. However, the sarcina granules proved too small to be retained effectively in the reaction zone. At a moderate VLR of 10–20 g COD/L · d, the sludge granules expanded into the settling zone and accumulated there; at 25 g COD/L · d, the sludge granules were lost excessively with effluent, and the reactor was unstable. Influent with concentrations of 1 000–5 000 mg COD/L is desirable for cultivation ofMethanothrix‐dominated, well‐settling, large granules.

ISSN:1061-4303    

DOI:10.2175/106143096X128540

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

The filterability parameters obtained from laboratory testing of cake filtration are discussed. A high‐quality filterability parameter for predicting full‐scale equipment operation should only exhibit a small change in parameter value with changing test conditions. An important factor is the test pressure applied, so, the discussion is based on the relationship between the filterability parameter and the test pressure. The traditionally used specific resistance to filtration (SRF) is shown to be highly dependent on the applied pressure when the compressibility of the investigated material is high. Therefore, in this case SRF looses its property as a material constant and a new parameter denoted the specific filtrate flow rate (SFF) is suggested as a possible alternative to SRF. A test coefficient (T) is derived to quantify the constancy of SRF and SFF in relation to changing test pressure. Data obtained from the literature are discussed in relation to SRF and SFF, and it is found that SFF is constant and thus the best alternative in case of biological wastewater solids and highly compressible inorganic slurries. However, for non‐ or slightly compressible solids SRF is more constant than SFF, and therefore, still the relevant filtration parameter. In the range of moderate compressibility neither SRF or SFF can be claimed constant.

ISSN:1061-4303    

DOI:10.2175/106143096X128568

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY

摘要:

A Cr(VI)‐reducing culture was enriched from an anaerobic chemostat fed with synthetic media containing acetate and Cr(VI). The enriched culture was used for a series of batch tests to investigate several environmental factors affecting microbial Cr(VI) reduction. Under carbon‐limiting conditions, the extent of Cr(VI) reduction proportionally depended on the carbon concentration and no reduction of Cr(VI) was observed in the absence of acetate. Cr(VI) reduction was also dependent upon the initial biomass level and the type of organic compounds. The developed model predicted Cr(VI) reduction well at different Cr(VI) concentrations.
Sulfate at 120 mg SO42−/L or nitrate at 150 mg N/L slightly inhibited Cr(VI) reduction. Reduction of nitrate but not sulfate was observed along with Cr(VI) reduction. Cr(VI) was not reduced by the aerobically growing culture, and it was found that oxygen inhibitory effects on Cr(VI) reduction were reversible. The optimum pH and temperature for Cr(VI) reduction were found to be 7.3 and 32°C, respectively. In addition, Cr(VI) reduction was sensitive to the metal ions that may coexist with Cr(VI) in industrial wastes containing Cr(VI).

ISSN:1061-4303    

DOI:10.2175/106143096X128586

出版商:Water Environment Federation    

年代:1996

数据来源: WILEY