Filtration properties of aerobic stabilized primary and mixed primary-chemical (alum) sludge

The filtration properties of aerobic stabilized primary and mixed primary-chemical (alum) sludges have been studied in terms of capillary suction time (CST), specific resistance to filtration and coefficient of compressibility. The sludges were taken from “continuous” flow laboratory aerobic digesters, with detention times ranging from 5 to 35 days held at 7, 12, 18 and 25°C.Specific resistance to filtration and capillary suction time for both primary and mixed primary-chemical sludge generally improved with increasing detention times in the digester, except for the sludges stabilized at 7°C which remained almost unchanged. Mixed primary-chemical sludge showed better filtration properties than primary sludge alone. A fairly good correlation was found between specific resistance to filtration and CST divided by percentage of suspended solids in the sludge sample. The sludge compressibility increased with increasing detention time in the digester for both types of sludges investigated. Anoxic storage of aerobically stabilized sludges caused an increase in specific resistance to filtration.     

Aerobic waste activated sludge (WAS) for start-up seed of mesophilic and thermophilic anaerobic digestion

Since there are very limited numbers of thermophilic anaerobic digesters being operated, it is often difficult to start up a new one using sludge from an existing reactor as a seed. However, for obvious reasons it seems few attempts have been made to compare the start-up performance of thermophilic anaerobic digestion using different sources of seed sludges. The purpose of this study was to evaluate the start-up performance of anaerobic digestion using aerobic waste activated sludge (WAS) from a plant which has no anaerobic digesters and mesophilic anaerobic digested sludge (ADS) as the seed source at both mesophilic (35 degrees C) and thermophilic (55 degrees C) temperatures. In this study, two experiments were conducted. First, thermophilic anaerobic reactors were seeded with WAS (VSS = 4400 mg/L) and ADS (VSS = 14,500 mg/L) to investigate start-up performance with a feed of acetate as well as propionate. The results show that WAS started to produce CH4 soon after acetate feeding without a lag time, while ADS had a lag time of 10 days. When the feed was changed to propionate, WAS removed propionate down to below the detection limit of 10 mg/L, while ADS removed little propionate and produced little CH4. Second, in order to further compare the methanogenic activity of WAS and ADS, both mesophilic and thermophilic reactors were operated. WAS acclimated to anaerobic conditions shortly (< 5 days at both mesophilic and thermophilic) and after acclimating it produced more CH4 per unit amount of seeded VSS than ADS. WAS at mesophilic temperature biodegraded acetate at the same rate as for thermophilic. However WAS at mesophilic temperature biodegraded propionate at a much faster rate than at thermophilic. WAS as the seed source of anaerobic digestion resulted in much better performance than ADS at both mesophilic and thermophilic temperatures for both acetate and propionate metabolism.     

Benthal stabilization of waste activated sludge

Laboratory studies were performed on the stabilization of waste activated sludge solids in a deposit formed at the bottom of an aerated water column. Conclusions reached were as follows: (1) As long as dissolved oxygen is maintained in the water column, the benthal process is stable and odor free. (2) At temperatures within the range of 20 ± 1°C, an average benthal stabilization rate of 79.4 g m⁻² d⁻¹ (biodegradable solids) can be attained if solids are not limiting. (3) Under conditions stated in conclusion (2), as much as 63% of total carbon stabilization can occur via methane formation. (4) A year-old benthal deposit of waste activated sludge solids can be expected to have a solids percentage of about 2.3%     

河道淤泥的流动化处理及其工程性质的试验研究

1　前　　言 在江南地区 ,遍布各种大小河道。过去 ,都是将河道内淤泥作为农田的有机肥料加以利用 ,客观上对河道进行了定期的清淤 ,从而保持了这些河道有一定的蓄水能力和通航能力。现在由于农村耕作方式的变化 ,已很少利用这些天然的有机肥料 ,从而使这些河道的淤积越来越严重。最近 ,基于环境保护的意识 ,开始实施对这些河道进行清淤 ,但清淤出来的淤泥处理问题并没有很好地解决。与此同时 ,在这些地区实施道路、桥梁、河堤、护岸等工程时 ,经常会遇到构筑物填筑材料短缺和软弱地基的问题。因此 ,如能将河道淤泥进行再生资源化利用并将它作为河堤、路堤等构筑物或软基换土处理的填筑材料使用 ,不仅可以降低工程成本     

污泥的固化稳定化技术综述

污泥的固化稳定化是污泥处理处置的热点问题,从固化材料角度综述了污泥的固化稳定化技术研究进展,并对今后污泥固化稳定化所走的道路提出展望。     

Aerobic degradation of sulfanilic acid using activated sludge

This paper evaluates the aerobic degradation of sulfanilic acid (SA) by an acclimatized activated sludge. The sludge was enriched for over three months with SA (>500 mg/L) as the sole carbon and energy source and dissolved oxygen (DO, >5 mg/L) as the primary electron acceptor. Effects of aeration rate (0-1.74 L/min), DO concentration (0-7 mg/L) and initial SA concentration (104-1085 mg/L) on SA biodegradation were quantified. A modified Haldane substrate inhibition model was used to obtain kinetic parameters of SA biodegradation and oxygen uptake rate (OUR). Positive linear correlations were obtained between OUR and SA degradation rate (R² ≥ 0.91). Over time, the culture consumed more oxygen per SA degraded, signifying a gradual improvement in SA mineralization (mass ratio of O₂: SA at day 30, 60 and 120 were 0.44, 0.51 and 0.78, respectively). The concomitant release of near stoichiometric quantity of sulphate (3.2 mmol SO₄²⁻ released from 3.3 mmol SA) and the high chemical oxygen demand (COD) removal efficacy (97.1%) indicated that the enriched microbial consortia could drive the overall SA oxidation close to a complete mineralization. In contrast to other pure-culture systems, the ammonium released from the SA oxidation was predominately converted into nitrate, revealing the presence of ammonium-oxidizing bacteria (AOB) in the mixed culture. No apparent inhibitory effect of SA on the nitrification was noted. This work also indicates that aerobic SA biodegradation could be monitored by real-time DO measurement.     

Effect of temperature on algal removal from wastewater stabilization ponds by alum coagulation

Questions about the effect of temperature on algal cell coagulation and the relationships between algae removal and temperature, alum dosage, paddle speed, flocculation time, and settling time are answered. The investigations consisted studies on algae in wastewater stabilization ponds. The jar-test technique was used for the coagulation of algal suspension by alum.Analysis of variance of the variables and their interactions showed significantly the effect of all variables and most of their interactions. Step-wise multiple regression technique was used for the development of mathematical models for the estimation of algal removal.Increased temperatures adversely affected the percentage removal of algal cells by alum coagulation. Alum was effective in removing algae from Logan wastewater stabilization ponds. However, high alum dosage are required which may not be justified economically.     

Effects of primary sludge particulate (PSP) entrapment on ultrasonic (20 kHz) disinfection of Escherichia coli

The role of primary sludge particulates (PSPs) in ultrasonic disinfection of Escherichia coli (E. coli) was investigated. Entrapment of E. coli by PSP was directly observed through scanning electron microscope (SEM) after E. coli and PSP were incubated together in water for 24 h at 35 °C. Entrapment coefficient was proposed for the first time to reflect the ability of PSP to entrap E. coli and was estimated as 1.4 × 10³ CFU/mg PSP under our experimental conditions. Ultrasonication (20 kHz) of different E. coli-PSPs solutions showed that the entrapped E. coli cells were protected by PSP from ultrasonication and the unentrapped cells were not. However, the protection of entrapped E. coli cells gradually decreased as ultrasonication proceeded, suggesting the ability of power ultrasonication to deprotect the entrapped E. coli cells. SEM studies suggested a two-step mechanism for ultrasonic (20 kHz) disinfection of entrapped E. coli: breakdown of the protective PSP refugia and disinfection of the exposed E. coli cells. This research will enable more informed decisions about disinfection of aqueous samples where porous PSP are present.     

Thermophilic anaerobic digestion of pulp and paper mill primary sludge and co-digestion of primary and secondary sludge

Anaerobic digestion of pulp and paper mill primary sludge and co-digestion of primary and secondary sludge were studied for the first time in semi-continuously fed continuously stirred tank reactors (CSTR) in thermophilic conditions. Additionally, in batch experiments, methane potentials of 210 and 230 m³CH₄/t volatile solids (VS)_added were obtained for primary, and 50 and 100 m³CH₄/tVS_added for secondary sludge at 35 °C and 55 °C, respectively. Anaerobic digestion of primary sludge was shown to be feasible with organic loading rates (OLR) of 1-1.4 kgVS/m³d and hydraulic retention times (HRT) of 16-32 d resulting in methane yields of 190-240 m³CH₄/tVS_fed. Also the highest tested OLR of 2 kgVS/m³d and the shortest HRT of 14-16 d could be feasible, if pH stability is confirmed. Co-digestion of primary and secondary sludge with an OLR of 1 kgVS/m³d and HRTs of 25-31 d resulted in methane yields of 150-170 m³CH₄/tVS_fed. In the digestion processes, cellulose and hemicellulose degraded while lignin did not. pH adjustment and nitrogen deficiency needs to be considered when planning anaerobic digestion of pulp and paper mill wastewater sludges.     

Benthal stabilization, a low-cost process for the stabilization of waste activated sludge solids

The benthal process is described and a procedure is developed for the rational design of the process for the stabilization of waste activated sludge solids. Kinetic data from another study are used in the application of the procedure to a design example. A benthal stabilization system is compared with two types of aerobic stabilization systems with respect to construction costs and power usage. The economic advantage of benthal stabilization is shown to be dramatic.     

Characterization of stainless steel pickling bath sludge and its solidification/stabilization

X-ray diffractometer analysis of stainless steel sulfuric acid pickling bath sludge shows that it contains FeCr₂O₄, NiCr₂O₄, NiCrO₄, and Cr₂O₃, which do not dissolve in the acids. X-ray fluorescent spectroscopy (XRF) study reveals that chromium concentration in the sludge is as high as in stainless steel, whereas nickel concentration is on lower side and iron is the major constituent of the sludge. Cement-sludge sand mortar cubes have been prepared in the laboratory. Compressive strength of these cubes decreases linearly with increase in sludge content. As per US EPA TCLP test, heavy metal (Cr and Ni) concentrations are negligible in leachate of cement-sludge sand mortar cubes at 28 days of curing. Hence, cement-sludge sand mortar cubes can be made for safe disposal of sludge.     

Aerobic batch degradation of 17-beta estradiol (E2) by activated sludge: effects of spiking E2 concentrations, MLVSS and temperatures

Aerobic batch degradation of 17beta estradiol (E2) spiked into the activated sludge liquor from a sewage treatment plant was studied; and the likely impacts of E2's initial concentrations (C0), microbial population densities (MLVSS) and temperatures (TEMPT) were examined for a variety of combinations of these three factors: C0 = 10, 30 and 50 microgl(-1); MLVSS = 1750, 875 and 435 mgl(-1); and TEMPT = 5, 20 and 35 degrees C. The results, together with those obtained through two control runs performed using a killed sludge sample, demonstrated clearly that E2 was eliminated from the aqueous phase readily under appropriate MLVSS and temperature levels, with the role of sorption by biomass being less significant. By fitting observed concentration data with a first-order rate expression, the degradation rate constants (k) under all experimental conditions were estimated. The magnitude of k changed markedly in the range of 0.23-4.79 h(-1), following a general order that the higher the MLVSS was, the higher the rate constant, and that the higher the temperature, the higher the rate constant. An obvious increasing trend of the biomass-modified average rate constant (k') with increases in the temperature was also presented: the k' values at 5, 20 and 35 degrees C were 0.79, 1.77 and 3.29l MLVSS g(-1)h(-1), respectively. Furthermore, based upon the estimated k values, the temperature coefficients (theta) over the ranges of 5-20 and 20-35 degrees C were determined. In similarity with the magnitude of theta reported for ordinary BOD-based organic matrices in domestic wastewater, the theta values of E2 varied in the range of 1.026-1.09, suggesting that the temperature impacts on the degradation rates of E2 and BOD constituents are probably similar.     

Aerobic digestion of thickened activated sludge: Reaction rate constant determination and process performance

The aims of this work were to select which parameter—total suspended solids (TSS), volatile suspended solids (VSS) or degradable volatile suspended solids (DVSS)—best expressed the kinetics of aerobic digestion of waste secondary activated sludge: to define the relationship between the reaction rate constant and the initial concentration of sludges; to evaluate the effect of aerobic digestion on the filterability of the treated sludge as measured by the capillary suction time (C.S.T.).Batch experiments of aerobic digestion were performed in our laboratory on samples of sludges at a constant temperature of 20 C. The initial concentration of sludges ranged from 2600 to 22,000 mg l⁻¹.TSS was found to be the parameter which most closely fits the kinetic model of aerobic digestion. The reaction rate constant was a linear, inverse function of the initial sludge concentration with TSS and with VSS as a parameter.Sludge filterability is affected by the process of aerobic digestion; a prolonged aeration time results in poorer dewatering; and the more concentrated the sample, the poorer the dewatering.     

Elutriated acid fermentation of municipal primary sludge

The performance of a novel fermentation process, adopting a sludge blanket type configuration, for higher hydrolysis/acidogenesis of the municipal primary sludge was investigated under batch and semi-continuous conditions with varying pH and temperature. This acid elutriation slurry reactor provided higher system performance with a short HRT (5d) and higher acidogenic effluent quality under pH 9 and thermophilic (55 degrees C) conditions. The hydrolysis of the sludge was revealed to be significantly dependent on seasonal effects for sludge characteristics but with little impact on acidogenesis. Based on the rainy season at the optimal conditions, VFA production and recovery fraction (VFA(COD)/COD) were 0.18 g VFA(COD)/g VSS(COD) and 63%. As byproducts, nitrogen and phosphorus release were measured at 0.006 g N/g VSS(COD) and 0.003 g P/g VSS(COD), respectively. For the mass balance in a full-scale plant (Q=158,880 m(3)/d) based on the rainy season, the VFA and non-VFA (as COD) production were 3110 kg VFA(COD)/d and 1800 kg COD/d, resulting in an increase of organics of 31 mg COD/L and 20mg VFA(COD)/L and nutrients of 0.7 mg N/L and 0.3 mg P/L in the influent sewage. The economical benefit from this process application was estimated to be about 67 dollars per 1000 m(3) of sewage except for energy requirements and also, better benefits can be expected during the dry season. Moreover, the results revealed that the process has various additional advantages such as pathogen-free stabilized solids production, excellent solids control and economical benefits.     

Effect of magnesium oxychloride cement on stabilization/solidification of sewage sludge

Solidification/stabilization (S/S) is considered to be a well-established disposal technique to reduce sludge handling and disposal obstacles. In this work, the sewage sludge was solidified at variable proportions with magnesium oxychloride cement (denoted as MOC thereinafter) as reagent. The mortar prism samples of 40 × 40 × 160 mm in dimension were prepared and hardened for 24 h at room temperature. Unconfined compressive strength after 10-day curing time, initial and final setting time, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and toxicity leachability of the samples, were used to characterize the macroscopic and microscopic effects caused by the solidified products on the MOC hydration process. The results revealed that the magnesium hydration of phase 3, phase 5 and other hydration components in CS developed a crystallizing network in the hydrated solidified products, which not only enhanced the strength of CS but also prevented the precipitation of heavy metal ions from CS.     

A cost-effective system for the aerobic stabilization and disposal of waste activated sludge solids

Five types of aerobic stabilization systems are compared with respect to construction cost, power usage, and operating features. Kinetic data for the aerobic stabilization of waste activated sludge solids are reviewed and evaluated. Guidelines are established for the rational design and operation of (1) a multicellular aerobic stabilizer, (2) a long-term (12 months) stabilized solids storage lagoon and (3) a dedicated land-disposal activity. Emphasis is placed on systems serving smaller treatment plants.     

Fate and distribution of pharmaceuticals in wastewater and sewage sludge of the conventional activated sludge (CAS) and advanced membrane bioreactor (MBR) treatment

In this paper we report on the performances of full-scale conventional activated sludge (CAS) treatment and two pilot-scale membrane bioreactors (MBRs) in eliminating various pharmaceutically active compounds (PhACs) belonging to different therapeutic groups and with diverse physico-chemical properties. Both aqueous and solid phases were analysed for the presence of 31 pharmaceuticals included in the analytical method. The most ubiquitous contaminants in the sewage water were analgesics and anti-inflammatory drugs ibuprofen (14.6-31.3 μg/L) and acetaminophen (7.1-11.4 μg/L), antibiotic ofloxacin (0.89-31.7 μg/L), lipid regulators gemfibrozil (2.0-5.9 μg/L) and bezafibrate (1.9-29.8 μg/L), β-blocker atenolol (0.84-2.8 μg/L), hypoglycaemic agent glibenclamide (0.12-15.9 μg/L) and a diuretic hydrochlorothiazide (2.3-4.8 μg/L). Also, several pharmaceuticals such as ibuprofen, ketoprofen, diclofenac, ofloxacin and azithromycin were detected in sewage sludge at concentrations up to 741.1, 336.3, 380.7, 454.7 and 299.6 ng/g dry weight. Two pilot-scale MBRs exhibited enhanced elimination of several pharmaceutical residues poorly removed by the CAS treatment (e.g., mefenamic acid, indomethacin, diclofenac, propyphenazone, pravastatin, gemfibrozil), whereas in some cases more stable operation of one of the MBR reactors at prolonged SRT proved to be detrimental for the elimination of some compounds (e.g., β-blockers, ranitidine, famotidine, erythromycin). Moreover, the anti-epileptic drug carbamazepine and diuretic hydrochlorothiazide by-passed all three treatments investigated.Furthermore, sorption to sewage sludge in the MBRs as well as in the entire treatment line of a full-scale WWTP is discussed for the encountered analytes. Among the pharmaceuticals encountered in sewage sludge, sorption to sludge could be a relevant removal pathway only for several compounds (i.e., mefenamic acid, propranolol, and loratidine). Especially in the case of loratidine the experimentally determined sorption coefficients (K_ds) were in the range 2214-3321 L/kg (mean). The results obtained for the solid phase indicated that MBR wastewater treatment yielding higher biodegradation rate could reduce the load of pollutants in the sludge. Also, the overall output load in the aqueous and solid phase of the investigated WWTP was calculated, indicating that none of the residual pharmaceuticals initially detected in the sewage sludge were degraded during the anaerobic digestion. Out of the 26 pharmaceutical residues passing through the WWTP, 20 were ultimately detected in the treated sludge that is further applied on farmland.     

Possible cause of excess sludge reduction in an oxic-settling-anaerobic activated sludge process (OSA process)

Modification of a conventional activated sludge process by inserting a sludge holding tank in a sludge return line forms an oxic-settling-anaerobic (OSA) process that may provide a cost-effective way to reduce excess sludge production in activated sludge processes. In this paper we systematically evaluate the following possible scenarios that may explain the reduction of excess sludge in the OSA process: (i). energy uncoupling, (ii). domination of slow growers, (iii). soluble microbial products (SMPs) effect and (iv). sludge decay in the sludge holding tank under a low oxidation-reduction potential (ORP) condition. Results show that only the final scenario may reasonably explain this reduction. It has also been found that the sludge decay process in the sludge holding tank may involve the reduction of the cell mass.     

Behaviour and occurrence of estrogens in municipal sewage treatment plants--II. Aerobic batch experiments with activated sludge

Aerobic batch experiments containing a diluted slurry of activated sludge from a real sewage treatment plant (STP) near Frankfurt/Main were undertaken, in order to investigate the persistence of natural estrogens and contraceptives under aerobic conditions. The batch experiments showed that while in contact with activated sludge the natural estrogen 17 beta-estradiol was oxidized to estrone, which was further eliminated in the batch experiments in an approximate linear time dependence. Further degradation products of estrone were not observed. 16 alpha-hydroxyestrone was rapidly eliminated, again without detection of further degradation products. The contraceptive 17 alpha-ethinylestradiol was principally persistent under the selected aerobic conditions, whereas mestranol was rapidly eliminated and small portions of 17 alpha-ethinylestradiol were formed by demethylation. Additionally, two glucuronides of 17 beta-estradiol (17 beta-estradiol-17-glucuronide and 17 beta-estradiol-3-glucuronide) were cleaved in contact with the diluted activated sludge solution and thus 17 beta-estradiol was released. The glucuronidase activity of the activated sludge was further confirmed by the cleavage of 4-methylumbelliferyl-beta-D-glucuronide (MUF-beta-glucuronide) in a solution of a activated sludge slurry and Milli-Q-water (1:100, v/v). The turnover rate obtained was approximately steady state, with a turnover rate of 0.1 mumol/l for the released MUF. Hence, it is very likely that the glucuronic acid moiety of 17 beta-estradiol glucuronides and other estrogen glucuronides become cleaved in a real municipal STP, so that the concentrations of the free estrogens increase.