Effect of steel slag in recycling waste activated sludge to produce anaerobic granular sludge.

The amount of waste activated sludge (WAS) has grown dramatically in China. WAS is considered as a problematic and hazardous waste, which should be disposed in a safe and sustainable manner. In order to recycle WAS to an anaerobic granular sludge (AnGS) process for anaerobic digestion, Fe powder and steel slags (rusty and clean slags) were used to enhance the granulation process. The results demonstrated that both rusty and clean slags encouraged the development of granular sludge. Adding 10 g/L clean slags could increase AnGS granulation rate by 37%. In the presence of clean slags, extracellular polymeric substances (EPS) concentration in granules increased noticeably to 715 mg/g mixed liquor suspended solids (MLSS). High throughput sequencing analysis exhibited more diversity and higher abundance of functional microbial communities in the batch bottle with 10 g/L clean slags. This study suggested that adding clean slags at 10 g/L dosage was a sustainable and effective method for the sludge granulation.

A new strategy to recover from volatile fatty acid inhibition in anaerobic digestion by photosynthetic bacteria.

The accumulation of volatile fatty acids (VFAs) can decrease reactor pH and inhibit methane-producing process. For the first time, photosynthetic bacteria (PSB) were used to recover from VFAs inhibition (pH 6.0) of an anaerobic digestion system. After adding PSB for 12 days with and without light condition, the methane content recovered from 33.3% to 60.5% and from 32.1% to 59.3%, respectively; the pH increased to 7.1 and 6.8, respectively, the system alkalinity rapidly increased to 2238 and 1921 mg/L, respectively; the sCOD decreased from 5600 to 995 mg/L and from 5575 to 2025 mg/L, respectively; and the contents of formic acid, acetic acid, propionic acid and total VFA were greatly reduced. Microbial analysis found that PSB bioaugmentation could maintain microbial diversity of the system. PSB bioaugmentation could effectively relieve acids accumulation and stimulate methane production especially under light condition. It is also found that light could accelerate recovery with or without bioaugmentation.

Effect of different initial low pH conditions on biogas production, composition, and shift in the aceticlastic methanogenic population.

Anaerobic digestion (AD) reactors often encounter low pH inhibition during startup and high organic loading periods. The use of a large amount of NaOH in order to raise and buffer the low pH, is reported to be inhibitory to methanogens. In order to address this problem, we acclimatized aceticlastic methanogens to low pH. Methanogens were successfully acclimatized to initial low pH down to 3.5 in a lengthy, five months, acclimatization period. The aceticlastic methanogen, Methanothrix soehngenii which was 96.3% of the total methanogenic population at pH 4.5 and 86.75% at pH 3.5, demonstrated that they were the most tolerant aceticlastic methanogens to low pH. After acclimatization, methane yield at pH 4.5 was comparable to neutral pH. Methanosaeta maintained its dominance over Methanosarcina at an elevated level of acetate (66 mM), and a negative correlation was observed between them. There was a positive correlation between the CH4 content and pH.

Variability of release rate of flame retardants in wastewater treatment plants.

Information on variability is important in the assessment of the releases and potential risks of brominated flame retardants (BRFs) in the environment, but related data are limited. In this study, two release-characterizing parameters, release fraction to final effluent and influent-biosolids transfer coefficient, were used to quantify releases of five BFRs from eight secondary wastewater treatment plants (WWTPs). The five BFRs are recalcitrant, hydrophobic, and low in volatility. The two parameters for these BFRs were found to vary from day to day and season to season within individual WWTPs as well as from one WWTP to another. These temporal and spatial variations were, however, comparable to each other and both within a factor of 3 above or below the parameter averages. Averages for release fraction were in the range of 0.02-0.29 and those for influent-biosolids transfer coefficient in the range of 3-26 L/g, depending upon a given BFR at a given WWTP. These ranges and the observed factor-3 variability are not only useful for estimating releases of the five BFRs, but more importantly provide read-across data for the assessment of substances with similar physical-chemical properties.

General Fate Model for Microconstituents in an Activated Sludge System.

Nine laboratory-scale continuous flow porous-pot bioreactors, operating at various solids retention times (SRT) and hydraulic retention times, were used to simulate activated sludge systems, and to evaluate biodegradation kinetic models for the fate of 17α-ethinylestradiol (EE2), bisphenol-A (BPA), and triclosan (TCS) at the µg/L range. Mathematical models were applied to describe the degradation mechanism of selected microconstituents and the pseudo-second-order model was found to best fit the results when active microconstituent degraders (XC) were used (r2 = 0.99). The result of XC estimation showed that SRT plays an important role in formation of the biomass capable of degrading selected microconstituents. It is also observed that microconstituent degraders are naturally present in an activated sludge system, even at low SRTs; however, the concentration of XC is dependent on SRT. It seems that biodegradation studies should incorporate XC, and not mixed liquor suspended solids concentration, in their kinetic formulations.

Microwave effects on soluble substrate and thermophilic digestibility of activated sludge.

Thickened waste-activated sludge (TWAS) was subjected to microwave pretreatment and athermal irradiation. The soluble phase of each type of TWAS pretreatment was subject to ultrafiltration in series using progressively smaller pore-size membranes (300, 100, 10, and 1 kDa) and biodegradability tests. Microwave pretreatment solubilizes a considerable amount of the suspended organic substrate, but athermal irradiation also causes solubilization of organic matter, although at a smaller scale than microwave. Proteins are particularly sensitive to athermal irradiation, and both microwave and athermal irradiation are capable of changing the size distribution of dissolved organic matter. Athermal irradiation and microwave have a substantially different effect on thermophilic anaerobic biodegradability of the various size fractions obtained after ultrafiltration. Slight inhibition and decrease in total biogas production was measured in some microwave tests. Athermal irradiation does not cause a decrease in maximum biogas production rate in any test and increases slightly biogas production.

Sorption-desorption and biosorption of bisphenol A, triclosan, and 17α-ethinylestradiol to sewage sludge.

To better understand the fate of microconstituents (MCs) in an activated sludge (AS) system, sorption, biosorption, and desorption studies were investigated at µg/L range for 17α-ethinylestradiol (EE2), bisphenol A (BPA), and triclosan (TCS). Batch experiments with activated and deactivated sludge originating from continuous flow porous pot reactors operating at solid retention times (SRTs) of 5, 10, and 15 days were conducted in order to investigate the sorption kinetics and distinguish physicochemical sorption and biosorption. The effect of SRT and the biomass concentration on sorption kinetics were also studied. Selected MCs showed high sorption affinity to the non-viable biomass during the first 30 min of the experiment, which was gradually reduced until equilibrium was reached. Desorption results showed two distinct stages, a very rapid desorption within 20 min followed by a slow desorption stage. Biosorption study indicated that the soluble concentrations of target compounds decreased rapidly for selected MCs similar to the sorption study; however, the soluble and solid phase concentrations continued to decrease slowly during the length of the experiment which indicates the possible biodegradation of these compounds in both phases. Finally, mathematical models were applied to describe the sorption mechanism and Freundlich sorption isotherms with values of 1/n close to 1 were found to best fit the results which demonstrate that all tested concentrations result on the linear part of the Freundlich isotherm. Calculation of the Freundlich constant, KF and distribution coefficient, Kd exhibited the greater tendency of EE2 and TCS for sorption, compared to BPA. The results of this study indicated that the SRT had a clear effect on the sorption kinetics where the highest sorption rate constant was achieved for a SRT of 10 days for all three target substances. This could be due to change of the morphology of the biomass from reactors operating at different SRTs.

Optimization of A(2)O BNR processes using ASM and EAWAG Bio-P models: model performance.

This paper presents the performance of an optimization model for a biological nutrient removal (BNR) system using the anaerobic-anoxic-oxic (A(2)O) process. The formulated model simulates removal of organics, nitrogen, and phosphorus using a reduced International Water Association (IWA) Activated Sludge Model #3 (ASM3) model and a Swiss Federal Institute for Environmental Science and Technology (EAWAG) Bio-P module. Optimal sizing is attained considering capital and operational costs. Process performance is evaluated against the effect of influent conditions, effluent limits, and selected parameters of various optimal solutions with the following results: an increase of influent temperature from 10 degrees C to 25 degrees C decreases the annual cost by about 8.5%, an increase of influent flow from 500 to 2500 m(3)/h triples the annual cost, the A(2)O BNR system is more sensitive to variations in influent ammonia than phosphorus concentration and the maximum growth rate of autotrophic biomass was the most sensitive kinetic parameter in the optimization model.

Mesophilic anaerobic digestion with high-temperature microwave pretreatment and importance of inoculum acclimation.

Thickened waste activated sludge (TWAS) was pretreated with microwave irradiation to temperatures higher than the boiling point (between 110 and 175 degrees C) using different microwave intensities. Biochemical methane potential (BMP) assays demonstrated that, although mesophilic anaerobic digestion (MAD) inoculum used was acclimated for 4 months with microwave pretreated TWAS (to 175 degrees C), acute methanogenic inhibition was observed. Additionally, the microwave conditions applied increased the soluble chemical oxygen demand (sCOD)-to-total COD (tCOD) ratio; however, no significant enhancement in the rate or extent of TWAS stabilization was observed for the microwave-pretreated samples. Microwave pretreatment to between 110 and 175 degrees C at lower microwave intensity with a better acclimated MAD inoculum (acclimatized for an additional 3 months) resulted in minimal methanogenic inhibition (improved acclimation) and improved the rate and extent of TWAS biodegradation, as determined by volatile solids removal and biogas production (microwave applied at lower microwave intensity). The TWAS pretreated to 175 degrees C produced 31 +/- 6% more biogas than the control (raw TWAS) by the 18th day of the BMP test, whereas the highest improvement observed from the first set of BMP experiments was 13 +/- 1%.

Evaluation of continuous mesophilic, thermophilic and temperature phased anaerobic digestion of microwaved activated sludge.

The effects of microwave (MW) pretreatment, staging and digestion temperature on anaerobic digestion were investigated in a setup of ten reactors. A mesophilic reactor was used as a control. Its performance was compared to single-stage mesophilic and thermophilic reactors treating pretreated and non-pretreated sludge, temperature-phased (TPAD) thermophilic-mesophilic reactors treating pretreated and non-pretreated sludge and thermophilic-thermophilic reactors also treating pretreated and non-pretreated sludge. Four different sludge retention times (SRTs) (20, 15, 10 and 5 d) were tested for all reactors. Two-stage thermo-thermo reactors treating pretreated sludge produced more biogas than all other reactors and removed more volatile solids. Maximum volatile solids (VS) removal was 53.1% at an SRT of 15 d and maximum biogas increase relative to control was 106% at the shortest SRT tested. Both the maximum VS removal and biogas relative increase were measured for a system with thermophilic acidogenic reactor and thermophilic methanogenic reactor. All the two-stage systems treating microwaved sludge produced sludge free of pathogen indicator bacteria, at all tested conditions even at a total system SRT of only 5 d. MW pretreatment and staging reactors allowed the application of very short SRT (5 d) with no significant decrease in performance in terms of VS removal in comparison with the control reactor. MW pretreatment caused the solubilization of organic material in sludge but also allowed more extensive hydrolysis of organic material in downstream reactors. The association of MW pretreatment and thermophilic operation improves dewaterability of digested sludge.

Stochastic calibration of riverine water quality models.

Though commonly used, the suitability of deterministic calibration criteria for stochastic model calibration and uncertainty analysis is unclear. The purpose of this paper is to examine the suitability, relative benefits, and substantial disadvantages of "deterministic-optimization" approaches, such as root mean square error (RMSE), in stochastic contexts. Three alternate calibration strategies that are suitable for stochastic modeling of water quality under uncertainty are proposed and then demonstrated. The three alternate strategies are the absolute relative error (ARE), weighted relative error, and stochastic exceedance calibration strategy. The findings suggest that potential improvements can be made to current calibration paradigms. The alternate calibration strategies, all of which are based on relative error, were found to match or exceed RMSE calibration strategies, in terms of overall performance, with the enhancement of superior model surface-response characteristics. Additionally, the application of more stringent ARE criteria offered greater improvement in the stochastic calibration response than increasing the RMSE threshold criteria. Several qualitative benefits of ARE and related metrics also were shown. Because many environmental systems and almost all water quality models are subject to substantial uncertainty, approaches such as those proposed hold substantial, widely applicable benefits.

Evaluation of continuous mesophilic anaerobic sludge digestion after high temperature microwave pretreatment.

Effect of microwave pretreatment (MW) high temperature (175 degrees C) and MW intensity to waste activated sludge digested with acclimatized inoculum in single- and dual-stage semi-continuous mesophilic anaerobic digesters at different sludge retention times (SRTs) (20, 10 and 5 days) were investigated. MW pretreatment led to similar sludge stabilization at low SRTs (5 and 10 days). Although lowering MW intensity slightly improved sludge solubilization, it had a negative effect on digestion at low SRTs. Single-stage digesters with MW pretreatment surpass dual-stage digesters performances.

Synergetic pretreatment of sewage sludge by microwave irradiation in presence of H2O2 for enhanced anaerobic digestion.

A microwave-enhanced advanced hydrogen peroxide oxidation process (MW/H(2)O(2)-AOP) was studied in order to investigate the synergetic effects of MW irradiation on H(2)O(2) treated waste activated sludges (WAS) in terms of mineralization (permanent stabilization), sludge disintegration/solubilization, and subsequent anaerobic biodegradation as well as dewaterability after digestion. Thickened WAS sample pretreated with 1gH(2)O(2)/g total solids (TS) lost 11-34% of its TS, total chemical oxygen demand (COD) and total biopolymers (humic acids, proteins and sugars) via advanced oxidation. In a temperature range of 60-120 degrees C, elevated MW temperatures (>80 degrees C) further increased the decomposition of H(2)O(2) into OH* radicals and enhanced both oxidation of COD and solubilization of particulate COD (>0.45 micron) of WAS indicating that a synergetic effect was observed when both H(2)O(2) and MW treatments were combined. However, at all temperatures tested, MW/H(2)O(2) treated samples had lower first-order mesophilic (33+/-2 degrees C) biodegradation rate constants and ultimate (after 32 days of digestion) methane yields (mL per gram sample) compared to control and MW irradiated WAS samples, indicating that synergistically (MW/H(2)O(2)-AOP) generated soluble organics were slower to biodegrade or more refractory than those generated during MW irradiation.

Performance of an overland flow system for advanced treatment of wastewater plant effluent.

Overland flow (OF) systems were evaluated and compared for advanced treatment of municipal and industrial effluents, including nutrients and nondegradable chemical oxygen demand (COD) removal. Three pilot plants were constructed at the Shahin Shahr Wastewater Treatment Plant (WWTP), Isfahan, Iran. Each pilot was assigned a specific wastewater and all were simultaneously operated for 8 months. Treatment of primary effluent, activated sludge secondary effluent, and lagoon effluent of textile wastewater was investigated at application rates (ARs) of 0.15, 0.25, and 0.35 m(3)m(-1)h(-1). During 5 months of stable operation after a 3-month acclimation period, mean removals of total 5-day biochemical oxygen demand (TBOD(5)), total COD (TCOD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP) and turbidity were 74.5%, 54.8%, 66.2%, 39.4%, 35.8%, and 67.7% for primary effluent; 52.9%, 52.9%, 66.5%, 44.4%, 39.8%, and 50.1% for activated sludge effluent; 65.7%, 58.7%, 70.3%, 41.7%, 41.3%, and 54.9% for textile wastewater lagoon effluent, respectively. The model of Smith and Schroeder, 1985. Field studies of the overland flow process for the treatment of raw and primary treated municipal wastewater. Journal of Water Pollution Control Federation 57, 785-794] was satisfactory for TBOD(5). For all treatment parameters a standard first-order removal model was inadequate to represent the data but a modified first-order model provided a satisfactory fit to the data. Based on the results of this study, it can be concluded that an OF system as advanced treatment had the ability to meet effluent discharge permit limits and was an economical replacement for stabilization ponds and mechanical treatment options.

Performance of anaerobic waste activated sludge digesters after microwave pretreatment.

Effects of microwave pretreatment on waste activated sludge (WAS) in mesophilic semicontinuous digesters with acclimatized inoculum at solids retention times (SRTs) of 5, 10, and 20 days are presented. Batch digesters determined optimum microwave temperature, intensity, WAS concentration, and percentage of WAS pretreated for highest WAS solubilization (soluble to total chemical oxygen demand ratio [SCOD:TCOD]) and biogas production. Pretreatment results indicated the potential to damage floc structure and release 4.2-, 4.5-, and 3.6-fold higher soluble proteins, sugars, and SCOD:TCODs compared with controls, with nucleic acid release. Pretreatment increased dewaterability and bioavailability of WAS with 20% higher biogas production compared with controls in batch digestion. In semicontinuous digesters, relative (to control) improvements in removals dramatically increased, as SRT was shortened from 20 to 10 to 5 days, with 23 and 26% higher volatile solids removals for WAS pretreated to 96 degrees C by microwave and conventional heating at a 5-day SRT.

Enhancement of batch waste activated sludge digestion by microwave pretreatment.

Batch anaerobic digesters were used to stabilize microwave (MW)-irradiated waste activated sludge (WAS). A low temperature range (50-96 degrees C) MW irradiation was applied. Effects of pretreatment temperature (T) and intensity (I), concentration (C) and percentage of sludge pretreated (PT) were investigated in a multilevel factorial statistical design containing 54 mesophilic batch reactors by monitoring cumulative biogas production (CBP). Variance analysis (ANOVA) determined that the most important factors affecting WAS solubilization were temperature, intensity, and sludge concentration. Improvements in CBP from WAS were significantly affected by sludge percentage pretreated, temperature, and concentration. Pretreatment resulted in 3.6 +/- 0.6 and 3.2 +/- 0.1 fold increases in soluble to total chemical oxygen demand (SCOD/TCOD) at high and low sludge concentrations, respectively. WAS, microwaved to 96 degrees C, produced the greatest improvement in CBP with 15 +/- 0.5 and 20 +/- 0.3% increases over controls after 19 d of digestion at low and high WAS concentrations. Dewaterability of microwaved sludge was enhanced after anaerobic digestion.

Application of non-linear automatic optimization techniques for calibration of HSPF.

Development of TMDLs (total maximum daily loads) is often facilitated by using the software system BASINS (Better Assessment Science Integrating point and Nonpoint Sources). One of the key elements of BASINS is the watershed model HSPF (Hydrological Simulation Program Fortran) developed by USEPA. Calibration of HSPF is a very tedious and time consuming task, more than 100 parameters are involved in the calibration process. In the current research, three non-linear automatic optimization techniques are applied and compared, as well an efficient way to calibrate HSPF is suggested. Parameter optimization using local and global optimization techniques for the watershed model is discussed. Approaches to automatic calibration of HSPF using the nonlinear parameter estimator PEST (Parameter Estimation Tool) with its Gauss-Marquardt-Levenberg (GML) method, Random multiple Search Method (RSM), and Shuffled Complex Evolution method developed at the University of Arizona (SCE-UA) are presented. Sensitivity analysis was conducted and the most and the least sensitive parameters were identified. It was noted that sensitivity depends on number of adjustable parameters. As more parameters were optimized simultaneously--a wider range of parameter values can maintain the model in the calibrated state. Impact of GML, RSM, and SCE-UA variables on ability to find the global minimum of the objective function (OF) was studied and the best variables are suggested. All three methods proved to be more efficient than manual HSPF calibration. Optimization results obtained by these methods are very similar, although in most cases RSM outperforms GML and SCE-UA outperforms RSM. GML is a very fast method, it can perform as well as SCE-UA when the variables are properly adjusted, initial guess is good and insensitive parameters are eliminated from the optimization process. SCE-UA is very robust and convenient to use. Logical definition of key variables in most cases leads to the global minimum.

Athermal microwave effects for enhancing digestibility of waste activated sludge.

A bench scale industrial microwave (MW) unit equipped with fiber optic temperature and pressure controls within pressure sealed vessels successfully simulated conventional heating (CH, in water bath). By identical temporal heat temperature profiles for waste activated sludge (WAS) samples, evaluation of the athermal effects of MW irradiation on WAS floc disintegration and anaerobic digestion was achieved. In a pretreatment range of 50-96 degrees C, both MW and CH WAS samples resulted in similar particulate chemical oxygen demand (COD) and biopolymer (protein and polysaccharide) solubilization and there was no discernable MW athermal effect on the COD solubilization of WAS. However, biochemical methane potential (BMP) tests showed improved biogas production for MW samples over CH samples indicating that the MW athermal effect had a positive impact on the mesophilic anaerobic biodegradability of WAS. BMP tests also showed that despite mild inhibition in the first 7d, MW acclimated inoculum digesting pretreated (to 96 degrees C) WAS, produced 16+/-4% higher biogas compared to the control after 15 d of mesophilic batch digestion. However, initial acute inhibition was more severe for non-acclimated inoculum requiring recovery time that was two times longer with only 4+/-0% higher biogas production after 17d. Inoculum acclimation not only accelerated the production of biogas, but also increased the extent of the ultimate mesophilic biodegradation of MW irradiated WAS (after 15-27 d).

Characterization of soluble organic matter of waste activated sludge before and after thermal pretreatment.

Microwave (MW) irradiation and conventional heating (CH) at 96 degrees C was successful in disrupting the complex waste activated sludge (WAS) floc structure and releasing extra- and intra-cellular biopolymers, such as protein and sugars from activated sludge flocs into soluble phase along with solubilization of particulate chemical oxygen demand (COD). Soluble CODs of CH and MW-irradiated WAS were 361+/-45% and 143+/-34% higher and resulted in 475+/-3% and 211+/-2% higher cumulative biogas productions (CBP) relative to the control at the end of 23 days of mesophilic anaerobic digestion, respectively. Ultrafiltration (UF) was used to characterize the soluble molecular weight (Mw) distributions of control (unpretreated), CH and MW-irradiated WAS. Depending on the Mw fraction, the range of substrate volumetric utilization rate increases from anaerobic digesters was between 94% and 84% for CH and 26-113% for MW compared to the control for the first nine days of the digestion. Digesters treating high Mw (>300 kDa) materials resulted in smaller biodegradation rate constants, k, indicating that microorganisms require a longer time to utilize high Mw fractions which are most likely cell wall fragments and exopolymers.

Pollution loads in urban runoff and sanitary wastewater.

While more attention has been paid in recent years to urban point source pollution control through the establishment of wastewater treatment plants in many developing countries, no considerable planning nor any serious measures have been taken to control urban non-point source pollution (urban stormwater runoff). The present study is a screening analysis to investigate the pollution loads in urban runoff compared to point source loads as a first prerequisite for planning and management of receiving water quality. To compare pollutant loads from point and non-point urban sources, the pollutant load is expressed as the weight of pollutant per hectare area per year (kg/ha.year). Unit loads were estimated in stormwater runoff, raw sanitary wastewater and secondary treatment effluents in Isfahan, Iran. Results indicate that the annual pollution load in urban runoff is lower than the annual pollution load in sanitary wastewater in areas with low precipitation but it is higher in areas with high precipitation. Two options, namely, advanced treatment (in lieu of secondary treatment) of sanitary wastewater and urban runoff quality control systems (such as detention ponds) were investigated as controlling systems for pollution discharges into receiving waters. The results revealed that for Isfahan, as a low precipitation urban area, advanced treatment is a more suitable option, but for high precipitation urban areas, urban surface runoff quality control installations were more effective for suspended solids and oxygen-demanding matter controls, and that advanced treatment is the more effective option for nutrient control.