Showing papers in "Water Environment Research in 1995"

Urban stormwater toxic pollutants: assessment, sources, and treatability

Abstract: This paper summarizes an investigation to characterize and treat selected stormwater contaminants that are listed as toxic pollutants (termed toxicants in this paper) in the Clean Water Act, Section 307 (Arbuckle et al., 1991). The first project phase investigated typical toxicant concentrations in stormwater, the origins of these toxicants, and storm and land-use factors that influenced these toxicants, and storm and land-use factors that influenced these toxicant concentrations. Of the 87 stormwater source area samples analyzed, 9% were considered extremely toxic (using the Microtox® toxicity-screening procedure). Moderate toxicity was exhibited in 32% of the samples, whereas 59% of the samples had no evidence of toxicity. Only a small fraction of the organic toxicants analyzed were frequently detected organics investigated (present in 23% of the samples). Vehicle service and parking area runoff samples had many of the highest observed concentrations of organic toxicants. All metallic toxicants analyzed were commonly found in all samples analyzed. The second project phase investigated the control of stormwater toxicants using using a variety of bench-scale conventional treatment processes. Toxicity changes were monitored using the Microtox® bioassay test. The most beneficial treatment tests included settling for at least 24 hours (up to 90% reductions), screening and filtering through at least 40-μm screens (up to 70% reductions), and aeration and/or photodegradation for at least 24 hours (up to 80% reductions). Because many samples exhibited uneven toxicity reductions for the different treatment tests, a treatment train approach was selected for the current projet phase. This current phase includes testing of a prototype treatment device that would be useful for controlling runoff from critical source areas (e.g., automobile services facilities)

Laboratory studies on the anaerobic sequencing batch reactor

Abstract: The anaerobic sequencing batch reactor (ASBR) is a newx high rate anaerobic process (U.S. Pat. No. 5,185,079) that has been under development by Dague and co-workers at Iowa State University. In the research reported in this paper, four, 12-L ASBRs of different configurations were operated at a constant temperature of 35°C. The objectives of the work were to evaluate the fundamental factors affecting solids separation in the ASBR, including reactor configuration, mixing (continuous versus intermittent), gas-production rate, mixed liquor suspended solids concentration, and bioflocculation-granulation, and to determine the effect of these factors on the performance of the ASBR treating a soluble, synthetic substrate (nonfat dry milk). The ASBRs were capable of achieving in excess of 90% soluble chemical oxygen demand (COD) reduction on the synthetic milk substrate over a range of COD loadings from 2 to 12 g/L.d at hydraulic retention times of 48, 24, and 12 hours. Reactor configuration is significant in the development of granular sludge. Relatively tall, slender reactors tended to select for granules better than the short, stout reactors. However, the shorter reactors were capable of accumulating higher concentrations of bioimass than were the tall reactors. Intermittent mixing was found to be preferable to continuous mixing from both COD removal and methane production standpoints

Subsurface flow wetlands : a performance evaluation

Abstract: This paper evaluates data collected by the authors as well as other individuals and agencies at operational subsurface flow constructed wetlands. The purpose of the evaluation was to identify the influence of hydraulic loading, organic loading, hydraulic residence time (HRT) on removal performance for biochemical oxygen demand (BOD), total suspended solids (TSS), nitrogen and phosphorus. The results indicate that BOD and TSS removal can be very effective at a relatively short HRT and that BOD removal exhibits a linear relationship with organic loading. Effective nitrogen removal requires a longer HRT and appears to be limited by the low oxygen availability in these systems. Phosphorus removal is also somewhat limited and ranges from 30 to 60 percent. Design models for these parameters are available or under development

Competition for substrate and space in biofilms

Abstract: Competition for substrate and space in biofilms was studied using a microelectrode technique and a micro-slicing technique. Three different kinds of biofilms were cultured using laboratory-scale, rotating drum biofilm reactors fed with synthetic wastewater. The measured concentration profiles provide direct experimental evidence of the competition in multispecies biofilms for substrates. Increases in organic loading or ammonium-nitrogen loading cause more consumption of oxygen, which results in competition for oxygen between heterotrophs and nitrifiers. Even in a pure nitrification system, heterotrophs, supported by soluble microbial products or metabolic products, could exist in the nitrification biofilm. Nitrifiers, however, have difficulty existing in the heterotrophic biofilms, and their populations were always 4 or 5 orders lower than those ofheterotrophs. It was found that the value of criterion for transition between oxygen and ammonium in nitrifying biofilms (S N /S DO ) was between 0.77 and 1.2, and the value decreased with an increase ofglucose loading. The competition for substrate in biofilms resulted in a stratified structure with nonuniform spatial distributions of biofilm properties, such as density, porosity, and effective diffusivity. This stratified structure in turn affects the substrate transfer and substrate competition within the biofilm. It was found that a certain biofilm system may not have only one penetration depth, corresponding to the critical thickness, for the whole range of biofilm thicknesses.

Particle‐associated coliform in secondary effluents: shielding from ultraviolet light disinfection

Abstract: In this research, the effectiveness of various blending and sonication techniques were investigated for extracting particle-associated coliforms from secondary effluent samples. The amount of shielding from ultraviolet disinfection afforded these coliforms by the particulates was then assessed. It was found that blending samples for 1.5 minutes at 19 000 rpm at 4°C in a mixture of chemicals (resulting in concentrations of 10 -6 M Zwittergent 3-12, 10 -3 M EGTA, 0.01 M Tris buffer, 0.1% peptone, and pH 7) resulted in the greatest recovery of particle-associated coliform, as detected by the multiple tube fermentation (MTF) test. Fragmentation of large flocs during homogenization, as evidenced by the change in particle size distribution, was most likely the responsible mechanism. Sonication proved ineffective. It was found that particle association and shielding of coliforms significantly affect accurate measurements of coliform density in secondary effluent using the standard MTF test and that significantly more coliforms may be present in disinfected secondary effluents than is indicated by the standard enumeration procedure.

Pilot- and full-scale two-phase anaerobic digestion of municipal sludge

Abstract: Two-phase anaerobic digestion tests were conducted at DuPage County, Ill., to ascertain if this process configuration would alleviate severe foaming and overloading conditions experienced by the existing high-rate digestion system. Pilot-scale two-phase digestion of activated sludge exhibited aggregated carbohydrate-protein-lipid and volatile solids (VS) reductions of more than 70%, and gas yield and gas production rate of 0.29 m 3 /kg VS.d and 2.2 volume per culture volume per day, respectively, at an hydraulic retention time 12 days and a loading rate of 4.7 kg VS/m 3 .d without any evidence of digester foaming; this performance was considerably better than that of high-rate digestion. Acid- and methane-phase digester culture development was completed in approximately a month. The acid-digester gases contained 67% CO 2 , 30% CH 4 , 2% nitrogen, 1% H 2 S compared with 30% CO 2 , 69% CH 4 , 0% N 2 , and 0.1% H 2 S in the methane-digester gases. The methane digester generated 90 volume percent to 95 volume percent of the system methane production. An enrichment culture of fermentative acidogens was established in the acid-phase digester, whereas the methane digester harbored a dominant population of methanogenic organisms. The, existing high-rate digestion system was converted to a two-phase digestion process

Transformation of organic matter in a gravity sewer

Abstract: Transformation of wastewater organic matter during 3 hours of transportation in an intercepting gravity sewer was measured. Dissolved and particulate fractions in terms of the specific organic pools: carbohydrate, protein, lipid, and volatile fatty acids were measured as well as dissolved organic carbon (DOC) and chemical oxygen demand (COD). The fate of dissolved organics in bulk water was the focus. Sampling was performed during dry weather periods, taking the residence time into account. The bulk-water dissolved oxygen concentration was between 0.1 and 5 mg/L but relatively constant during each sampling period. Considerable removal of dissolved organics took place, with dissolved carbohydrate and acetate as the primary compounds removed. In COD units, the maximum measured value of the total changes in carbohydrate, protein, and acetate was 20 mg/L.h at 15 o C. The DOC removal rates were slightly higher than what could be explained by the total changes of the dissolved specific pools. The removal of dissolved carbohydrate was dependent on concentration level and temperature. Described as a first-order reaction, the removal rate (k) for dissolved carbohydrate was 0.58 h -1 and 0.27 h -1 at 15 o C and 8 o C, respectively. No net removal of particulate matter during transportation was found. There was evidence to conclude that growth of microorganisms took place because of a net removal of dissolved organics. From simple calculations, it was concluded that the possible removal of particles because of sedimentation during dry weather was in the same range as the growth. The observed change in wastewater composition during transportation in a gravity sewer affected the quality and the quantity of the organic matter and may be of importance for the biological nitrogen and phosphorus removal in wastewater treatment because a considerable part of the easy degradable fraction was removed

Measurement of bound water in sludges: A comparative study

Abstract: The centrifugal settling, expression, differential scanning calorimetry (DSC), and drying tests are employed for measuring the bound water content in a sludge made of CaCO 3 , PVC, or glass powders, an inorganic Cu(OH) 2 sludge, and an activated sludge. The bound water is found to be an operationally defined value that differs greatly when different measurement technique is applied.A classification scheme for dividing the moisture content in a sludge based on the bound water data is proposed

Control of volatile organic compound emissions using a compost biofilter

Abstract: Laboratory and field experiments were conducted using a pilot-scale compost biofilter (approximately 5.7 m 3 /min) to determine the potential of using biofiltration for removing volatile organic compounds (VOCs) from gas streams at publicly owned treatment works. Six compounds commonly found in wastewaters (benzene, trichloromethane, dichloromethane, toluene, tetrachloroethene, and trichloroethene) were selected for quantitative evaluation of removal efficiency. Gas fluxes through the biofilters ranged from 0.3 to 1.8 m 3 /m 2 .min with corresponding pressure drops of 0.1 to 0.7 kPa. Removals of aromatic VOCs averaged greater than 80% during an 8.5-month field study and were typically greater than 90 to 95%, despite highly variable inlet concentrations. Removals of chlorinated VOCs were inconsistent and ranged from none to more than 60%. Low removals of the chlorinated compounds were believed to be due, in part, to the low inlet airstream concentrations, which were generally less than 70 ppb. Removal of H 2 S and odors was excellent throughout the studies, consistent with the findings of other investigators.

Evaluation of immobilized biomass beads for removing heavy metals from wastewaters

Abstract: Immobilized biomass beads, which consist of dried and ground sphagnum peat moss immobilized in a porous polysulfone matrix, effectively remove heavy metals from wastewaters under appropriate conditions. This paper examines the procedure for forming the beads and their performance in packed columns. The beads are produced by atomizing an organic dispersion into water, creating droplets that become solid through phase inversion. Increasing the relative biomass content gave slightly lower surface areas. Metal ion breakthrough curves were obtained for metal ions from two actual acid mine drainage wastewaters. The selectivity of the beads for various cations was Fe > Al > Pb > Cu > Cd, Zn > Ca > Mn > Mg > Na. Capacity increases with initial pH of the column after regeneration. Bead titration tests indicate that the immobilized biomass beads have heterogeneous ionogenic adsorption sites. Experimental results also indicate that most of the magnesium removed from water by the immobilized biomass beads is adsorbed and exchangeable with potassium. Under the conditions used here, the immobilized biomass beads have a lower capacity than two commercially available ion exchange resins.

Wastewater solids fermentation for volatile acid production and enhanced biological phosphorus removal

Abstract: Fermentation of wastewater solids for volatile acid (VA) production was studied as part of a full-scale demonstration of the Orange County Water and Sewer Authority (OWASA) process for enhanced biological phosphorus removal (EBPR). The VA yields in bench-scale fermentation tests ranged between approximately 6% and 26% of feed volatile solids (VS) under a range of test conditions that included solids retention times (SRTs) between 2 and 6 days, fermenter solids concentrations between 0.43% and 2.6%, and temperatures between 14 o C and 23 o C. Higher VA yields were observed at higher SRTs, lower fermenter solids concentrations, and higher temperatures. Settleability tests indicated that gravity separation of fermented sludge may be limited to an underflow concentration of 3%. After blending a phosphorus-rich waste activated sludge (WAS) with fermented primary solids, up to 42% of the WAS phosphorus was released within 5 hours. Two full-scale demonstration fermentation designs were investigated during the study that included a 2-month simultaneous testing period. Demonstration Fermenter No. 1 used rectangular dissolved air flotation thickeners that were retrofitted with submersible mixers, liquid-solids separation zones, and covers for odor control. This unit proved difficult to operate and maintain because of the design of the unit and the demanding duty. During the 2-month side-by-side test period, the VA yield averaged 0.05 mg/mg VS fed to the unit. The average VA composition of the fermenter product stream consisted of 41 no acetic acid, 44% propionic acid, 9% butyric acid, and 5% valeric acid. Suspended solid, organic, and nutrient loads in the fermenter product stream averaged 3.1 mg solids/mg VA, 1.7 mg carbonaceous biochemical oxygen demand (CBOD 5 )/mg VA, 0.04 mg ammonia/mg VA, and 0.05 mg phosphorus/mg VA during the 8-month testing period. The second fermenter used an existing sludge-holding tank mixed intermittently with coarse bubble aeration and dewatering centrifuges for liquid-solids separation. Demonstration Fermenter No. 2 proved to be quite reliable, although it provided less discretionary control over the fermentation process compared with Fermenter No. 1. During the side-by-side test, the VA yield averaged 0.05 mg/mg VS fed to the unit. The VA composition of the fermenter product stream averaged 38% acetic acid, 36% propionic acid, 16% butyric acid, and 10% valeric acid. During the 10-month testing period, the solid, organic, and nutrient loads averaged 1.0 mg solids/mg VA, 2.4 mg CBOD 5 /mg VA, 0.15 mg ammonia/mg VA, and 0.11 mg phosphorus/mg VA in the fermenter product stream. Both demonstration fermenters produced an acceptable quality VA source for use in a 22 000 M 3 /day (6 mgd) full-scale demonstration of the OWASA EBPR process. Performance of bench-scale and full-scale demonstration fermenters was highly variable (0.05 to 0.2 mg VA/mg VS feed). Commercial acetic acid was also used as the sole volatile acid source and as a supplement to the VA stream produced from the demonstration fermenters to stabilize EBPR performance

The effect of hydrogen peroxide on the degradation of methyl and ethyl tert-butyl ether in soils

Abstract: The degradation of the gasoline oxygenates, methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) in soil systems was evaluated. The data indicated that MTBE and ETBE were chemically oxidized to tertiary butanol and acetone when H 2 O 2 was added to soil microcosms containing aquifer material from an organic rich site. Identical reactions were observed when H 2 O 2 was added to solutions containing soluble ferrous iron and either MTBE or ETBE. Chemical oxidation was influenced by the H 2 O 2 concentration, pH, and the presence of ferrous iron but was independent of the iron concentration. Naturally occurring aerobic microcosms in the soil were able to degrade ETBE but not MTBE. Chemical oxidation coupled with an aerobic-anaerobic-biological cycle is proposed to describe a degradation pathway for ETBE in H 2 O 2 amended soils.

Water quality changes during soil aquifer treatment of tertiary effluent

Abstract: This paper summarizes the results of field studies in Tucson, Arizona, to estimate the soil aquifer treatment (SAT) effectiveness of a 5.7-ha (14-acre) water spreading facility, the Sweetwater Underground Storage and Recovery Facility. Groundwater samples collected from the facility during 1989 to 1990 were analyzed for pathogens. A specific basin was selected during the 1990 to 1991, 1991 to 1992, and 1992 to 1993 recharge seasons for sampling source water (tertiary effluent), pore-liquid samples from the vadose zone, and groundwater during recharge. These samples were analyzed for the nitrogen species, dissolved organic carbon (DOC), and total organic halide (TOX). The results showed that the site provides effective SAT. Enteroviruses were completely removed during travel in the 37-m (120-ft) thick vadose zone. No Giardia ware detected in any of the groundwater samples. The DOC and TOX were reduced by 92% and 85%, respectively. After leaching of indigenous nitrogen from the vadose zone, total nitrogen was reduced by approximately 47% during recharge. Near-surface anaerobic conditions promote denitrification

Treatment of seafood‐processing wastewaters in mesophilic and thermophilic anaerobic filters

Abstract: Wastewaters from fish-canning industries have a high concentration of organic polluting substances (10-50 g chemical oxygen demand L_1 [COD]) and, in some cases, a high content of sea salts (CL: 8-19 g L-', Na+: 5-12 g L\ SO^": 0.6-2.7 g L"1). The presence of high sodium ion concentrations in wastewaters with high organic content traditionally is considered as a very negative factor for their anaerobic treatment. In fact, both the presence of Na+ and SO4-, transformed into H2S during the anaerobic degradation process, may cause toxicity and inhibition on the methanogenic process. This work deals with the operation and treatment efficiency of two lab-scale mesophilic and thermophilic anaerobic filters (MAF and TAF, respectively). So that the adaptation of anaerobic sludge to high saline concentrations is attained, a prolonged start-up period of about nine months was necessary. After this, a stable operation and similar treatment efficiencies were reached, even when organic loading rate (OLR) as high as 9 kg COD irT3 d"1 (TAF) or 24 kg COD irT3 d_1 (MAF) were applied at chloride concentration of 13 g L-1. At these conditions, the COD removal reached 73% (TAF) and 64% (MAF), and the COD methanized reached 69% (TAF) and 66% (MAF). The sulphate in the influent was removed practically completely, leading to a H2S concentration in the biogas between 3-4%. In spite of the lower specific activity of sludge from MAF (0.21 g COD g"1 volatile suspended solids [VSS] d_1) than from TAF (0.66), the MAF reached a higher OLR than TAF. This fact can be explained because of the higher retention of sludge into MAF (72 g VSS L"1) than TAF (10 g VSS L_1). Two practical conclusions may be derived from this work: the thermophilic operation needs the use of a packing material with a higher capacity to retain biomass and the mesophilic operation requires a more frequent detachment of biomass from the support in order to avoid clogging problems. Water Environ. Res., 66, 000 (1994).

Development of refined clarifier operating diagrams using an updated settling characteristics database

Abstract: An analysis of five sludge-settling characteristics data sets is presented, representing data from 51 separate suspended growth bio logical wastewater treatment processes and including 214 separate runs and over 1 500 individual data points. The results indicate that the data can be characterized using a single relationship between the initial sludge settling velocity ( Kj), the initial sludge concentration (Ci), and the sludge volume index (SVI). The predictive capability of this relationship is in dependently verified. These results suggest that this single relationship can be used to accurately characterize the settling characteristics of an activated sludge based only on the measured SVI. A comparison of al ternate sludge-settling indexes indicates that the predictive capability of the relationship can be further improved by use of the stirred SVI3 5 analysis rather than the SVI. More data are required to refine relationships developed based on the SSVI3 5 and the diluted SVI. Secondary clarifier operating diagrams based on the developed relationships are presented. Water Environ. Res., 67, 000 (1995).

Performance of subsurface flow wetlands with batch-load and continuous-flow conditions

Abstract: Use of constructed wetlands designed for wastewater treatment is becoming common throughout the world. Oxidation of carbon (C) and nitrogen (N) may be increased by transport of oxygen (O 2 ) into the rhizosphere of aquatic plants and periodic draining of the wetland. Outdoor microcosms of subsurface flow wetlands (SFs) were operated receiving continuous flow or batch loads of primary and secondary wastewater. Six-square meter microcosms planted with Scirpus pungens, received primary or secondary wastewater in batch load or continuous flow. Plants in SFs had significant effects on C and N oxidation, whereas, periodic draining of SFs had no significant effect. Greater than 90% carbonaceous biochemical oxygen demand (CBOD) was removed within 18 hours in SFs with and without plants, after 6 and 12 hours plants had caused significant decreases in CBOD in the batch-load SFs. The first-order model for CBOD removal was not appropriate after 24 hours; removal rate coefficients were similar for batch-load and continuous-flow SFs with hydraulic retention times of 12 and 24 hours. Methanogenesis is the major respiratory pathway for CBOD removal. Oxygen transport in SFs estimated from C oxidation was 28.6 and 2.4 g/m 2 .d estimated from N oxidation.

Kinetics of pathogen destruction during storage of dewatered biosolids

Abstract: The kinetics of pathogen destruction were determined during storage of digested and dewatered wastewater treatment biosolids to obtain relationships between temperature and duration of biosolids storage. Biosolids, seeded with Salmonella typhimurium. Yersinia enterocolitica. Campylobacter jejuni, bacteriophage f2, poliovirus, and Ascaris suum eggs were incubated at 5 o , 22 o , 38 o , and 49.5 o C, under both aerobic and anaerobic conditions for up to 62 days. Destruction of pathogens in stored biosolids occurred at all temperatures examined; however, rates increased with increasing temperature. There was no significant difference between the destruction of pathogens under aerobic or anaerobic conditions at all temperatures studied. At 50 o C, the decay rate of S. typhimurium, Y. enterocolitica, bacteriophage f2, poliovirus, and A. suum eggs was estimated to be 1.13, 1.10, 1.54, 0.81, and 0.21 log 10 reductions per day, respectively

Interactions among sulfate reducers, acetogens, and methanogens in anaerobic propionate systems

Abstract: The complex process of propionate oxidation in anaerobic systems in the presence of excess sulfate is based on combinations of six biological reactions. Laboratory batch and continuous experiments were conducted to study which of these reactions were predominant in propionate oxidation by sulfate-reducing bacteria in the presence of acetogens and methanogens. The engineering significance of the feed propionate to sulfate ratio was studied. In batch serum bottle expriments, sulfide was more toxic to sulfate-reducing bacteria (SRB) than to acetogens and methanogens. Acetate was the least favored substrate for sulfate reduction. Two mechanisms appear possible under sulfate-limited conditions: (1) propionate use by both SRB and non-SRB acetogens and acetate and hydrogen use by methanogens and (2) propionate us by non-SRB acetogens followed by acetate use by methanogens and hydrogen use by both SRB and methanogens. In the chemostats, at a feed propionate:sulfate ratio of 2.2 (sulfate-limited condition), the acetate formed was primarily used by methanogens. With a gradual decrease in feed propionate:sulfate ratio from 2.2 to 0.44 (sulfate-rich condition), SRB outcompeted methanogens for acetate. In the chemostat study un-ionized H 2 S concentrations of up to 178 mg S/L (total sulfide 464 mg S/L) did not inhibit ssulfate reduction

Treatment of 2,4-dinitrotoluene using a two-stage system: Fluidized-bed anaerobic grangular activated carbon reactors and aerobic activated sludge reactors

Abstract: Continuous-flow anaerobic fluidized-bed granular activated carbon bioreactors were used to treat 2,4-dinitrotoluene (2,4-DNT), a compound used in primary propellant production. A synthetic wastewater solution containing 2,4-DNT, ethanol, mineral ether, and a carbonate buffer and another solution containing growth nutrients and vitamins were fed to each of the two bioreactors. The influent ethanol concentrations were varied to determine the effect of ethanol concentration on the extent of 2,4-DNT degradation. The anaerobic bioreactors, when operated under methanogenic conditions with a primary substrate, were able to transform the 2.4-DNT into 2-amino-4-nitrotoluene (2-A-4-NT). 4-amino-2-nitrotoluene (4-A-2-NT), 2,4-diaminotoluene (2,4-DAT), and trace amounts of toluene. During stable operation, for the range of non-zero influent ethanol concentrations evaluated in this study, the majority of the products were identified as 2,4-DAT. Batch activated sludge reactors were used to examine the fate of 2,4-DAT under aerobic conditions. 2,4-DAT (16 mg/L) were mineralized within 9 hours, indicating that a two-stage system may be an effective 2,4-DNT treatment strategy.

Stimulation of activated sludge cultures for enhanced heavy metal removal

Abstract: The objective of this research was to investigate the feasibility of developing improved activated sludge cultures capable of removing heavy metals present in high concentrations. Bacterial acclimation and stimulation with special chemicals were employed to this end. Thus, cystine, peptone, and β-glycerophosphate stimulated heavy metal uptake without a drastic reduction in culture viability otherwise experienced in the absence of these special nutrients. Acclimated-stimulated cultures substantially increased metal removal capabilities of aerobic cultures probably because of enhanced synthesis of metal-complexing biopolymers in the presence of precursor chemicals. The lethal effect of heavy metals could also be reduced significantly by culture development in the presence of these nutrients. The peptone-grown culture exhibited the highest removal of copper and cadmium of 0.65 and 0.68 mg/mg protein, respectively. This research shows that substantial improvements in the metal uptake capabilities of activated sludge cultures may be effected by including special nutrients (precursor biochemicals) with the process feed.

Criteria for nitrification and denitrification of high-strength wastes in two upflow submerged filters

Abstract: Design criteria for nitrification and denitrification of high-strength wastewaters are presented in two upflow submerged filters in series. Oxygen was a very important parameter effecting the ammonia removal rate in nitrification. The half-order and zero-order rate constants for nitrification were determined for the dissolved oxygen ranges of 2 to 3 mg/L and 4 to 5 mg/L, respectively. The transition from ammonia to oxygen rate limitation occurred at a bulk oxygen:bulk ammonia ratio of approximately 2.5 to 4, showing that nitrification was oxygen limited for practical purposes. In nitrification nitrite accumulation reached a considerable degree at bulk oxygen:bulk ammonia ratios lower than 5. Also, in denitrification the half- and zero-order rate constants were determined. The nitrite produced in the nitrification stage could be successfully reduced in denitrification without causing any inhibitory effect

Composition and variability of leachate from recent and aged areas within a municipal landfill

Abstract: A leachate study was conducted at a large, operating, regional municipal solid waste (MSW) landfill near Seattle, Washington, to examine differences in composition and emission rates between old and new areas of the fill. The landfill began operation in 1966, was receiving approximately 2000 tpd of MSW and had 30×10 6 m 3 (∼12×10 6 tonnes) waste in place at the time of this study. The two areas studied had average ages of 3.7 and 16 years, and contained 5.7×10 6 and 2.04×10 6 tonnes of MSW, respectively. Variations in flow rate, total dissolved solids (TDS), chemical oxygen demand (COD), total organic carbon (TOC), Fe, and Mn were monitored over a 3-month period in the winter and spring of 1992. Increases in flow driven by precipitation caused gradually increasing leachate mass emissions from the aged fill. The rate of mass emission increase with increasing flow from the new fill was more than three times higher than that from the old fill. Leachate flow through the old fill appeared more channelized, resulting in diluting effects with increasing percolation. In leachate from the new fill concentrations were essentially independent of flow. Overall, mass emissions per unit waste mass in place decreased with increasing waste age for TDS and Mn, indicating that these components were leachable independent of degradation processes. Mass emissions per unit waste mass in place increased with increasing waste age for COD, TOC, and Fe, which typify components that increase in availability for leaching with increasing age and progressing stage of decomposition

Oxidation of simazine: ozone, ultraviolet, and combined ozone/ultraviolet oxidation

Abstract: A laboratory study was conducted to investigate the kinetics and byproducts of simazine oxidation by ozone, ultraviolet radiation (UV), and combined ozone and UV. Byproducts were identified by HPLC. Simazine was oxidized rapidly by ozone, UV, and ozone and UV. For example, 4 mg/L simazine disappeared completely after oxidation by 34 mg/min ozone at pH 7.2 for 15 minutes. Simazine disappearance rates during ozonation increased with applied ozone dose and pH. Dealkylation and dechlorination byproducts were formed, and deamination byproducts appeared at higher ozone doses or higher pH. During UV and ozone and UV oxidation, simazine disappearance rates increased with UV intensity. Dechlorination byproducts were formed by UV oxidation. Dialkylation, deamination, and dechlorination byproducts were formed combined ozone and UV treatment. In comparing oxidation systems, simazine disappearance rates during oxonation at pH 9.9 were similar to those observed during ozone UV oxidation

Development of settling flux curves using SVI: an addendum

Abstract: An earlier paper by the authors (1988) introduced a correlation between the Vesilind settling parameters, V o and K, and SVI performed in a stirred, I-L graduated cylinder even though SVIs also were determined in more commonly used containers such as an unstirred, I-L graduated cylinder and an unstirred, 2-L Mallory settlometer. Only the stirred graduated cylinder relationship was given because stirring increases the precision and decreases the variability of the SVI test, and Standard Methods (1975) has included stirring in the SVI test since 1975. Nonetheless, because the SVI test continues to be performed in unstirred containers, the correlations for the other SVI test methods measured during the study are presented herein so that they can be used by the wastewater treatment plant operations community.

Measurement of dissolved free and combined amino acids in unconcentrated wastewaters using high performance liquid chromatography

Abstract: Dissolved free amino acids (DFAA) and dissolved com bined amino acids (DCAA, e.g., discrete dissolved polypeptides and pro teins as well as amino acids, peptides, and proteins adsorbed to humic material) were measured in unconcentrated domestic wastewater at a detection limit of 10 to 100 nM (coefficient of variation 70% for DFAA and 23% to 79% for DCAA. Molecular weight separations indicated that most dissolved organic carbon (DOC) (>68%) in the trickling filter influent had small molecular weights ( 10 000 AMU). The DTAA were a small fraction (8% to 13%) of DOC in both influent and effluent samples. Water Environ. Res., 67, 000 (1995).

Modeling the fate of pesticides in municipal wastewater treatment

Abstract: The fate of two insecticides (lindane and diazinon) and three herbicides (2,4-D, 2,4,5-T, and atrazine) in municipal wastewater was investigated in pilot plant experiments. The pesticides were dosed into the wastewater to provide feed concentrations in the 2 to 10 μg/L range. The pilot plant was operated at both 4- and 10-day solids retention times (SRTs) in the first of two testing campaigns and at a 4-day SRT in the second campaign. Only lindane was found to be biodegradable to any extent. Loss of pesticides from the system due to sorption to mixed liquor solids was small. Estimated partition coefficients ranged from 0.01 to 2 L/g volatile suspended solids (VSS), whereas biodegradation rates ranged from 0.1 for lindane to 4 E-6 L/g VSS.h for 2,4,5-T. Because the pesticides examined are mostly refractory to activated sludge treatment under the conditions examined, it is desirable to limit their entry to wastewater collection and treatment systems to minimize their impact on receiving waters.

Enumerating Salmonella in biosolids for compliance with pathogen regulations

Abstract: Recently adopted federal regulations (40CFR Part 503) for land use of biosolids set maximum bacterial limits based on fecal coliform or Salmonella and specified test methods to be used. The cited Salmonella methods were not evaluated for their suitability for compliance testing before inclusion in the regulation. This study evaluated the Part 503 Salmonella methods and two other Salmonella methods previously developed to test biosolids and compost. Ten samples each of activated sludge, anaerobically digested biosolids, and compost ware analyzed by five different procedures. Statistical analysis (Kruskal-Wallis one-way analysis of variance) indicated there was a significant difference between methods (P<0.001). Pairwise comparisons (Student-Newman-Keuls method) showed that the two methods that had been developed for testing biosolids were not significantly (P<0.05) different and recovered significantly (P<0.05) more salmonellae than the 503 cited methods. One 503 method failed to detect Salmonella in 43% of samples containing salmonellae. Only one of the three 503 spectified Salmonella test methods appeared acceptable for compliance testing