Aspects of the determination of complexation parameters for metal-particulate complexes in activated sludge

The conditional stability constants and complexation capacities for complexation of copper and lead by activated sludge solids have been determined by titration. The methods used were direct determination of free metal ion using ion selective electrodes and separation of the solids by membrane filtration prior to determination of the free metal in the filtrate. The complexation parameters thus obtained were compared and the importance of several factors, including residual metal concentrations in the sample prior to titration, interferences and the disturbances of complex equilibria during sample manipulation were examined and their potential effects on the calculated values of the complexation parameters were considered.     

Phosphorus removal in the activated sludge process

The results from this research suggest that both calcium phosphate precipitation and enhanced biological uptake play a role in phosphorus removal in the activated sludge process when a non-nitrifying, anaerobic-aerobic system is used to treat a low calcium wastewater. The primary removal mechanism was found to be biological uptake, as calcium phosphate precipitation accounted for only 15–27% of the total phosphorus removed. Calcium phosphate precipitation in the aerobic unit was enhanced because of the pH increase in that reactor. This was the result of low CO₂ production (indicated by low specific oxygen uptake values) and intense aeration which caused excessive CO₂ stripping in the aerobic unit     

Inhibition of the activities of β-galactosidase and dehydrogenases of activated sludge by heavy metals

Heavy metal inhibitions of the activities of β-galactosidase and dehydrogenases in activated sludge were studied.The activities of β-galactosidase and dehydrogenases were strongly inhibited by Cd and Hg. To produce 50% inhibition of β-galactosidase by Cd and Hg required 1.3 and 0.004 mmol g⁻¹ MLSS, respectively. In the case of dehydrogenase, 50% inhibition appeared by Cd 0.16 and Hg 0.04 mmol g⁻¹ MLSS, respectively.The inhibitions of the activities of β-galactosidase and dehydrogenases with Cd and Hg were easily recovered with the addition of thiol compounds. Reactivation by thiols suggested that Cd and Hg form reversible mercaptides with SH groups of β-galactosidase and dehydrogenases.The inhibitions of the activities of β-galactosidase and dehydrogenases by Cd and Hg gave reversible non-competitive type of kinetics. The inhibitor constant (K_i) values of β-galactosidase for Cd and Hg were calculated to be 1.6 mM (1.7 mmol g⁻¹ MLSS) and 0.005 mM (0.005 mmol g⁻¹ MLSS), respectively. K_i values of dehydrogenases for Cd and Hg were 0.6 mM (0.3 mmol g⁻¹ MLSS) and 0.02 mM (0.01 mmol g⁻¹ MLSS), respectively.     

Powdered activated carbon in an activated sludge treatment plant

Addition of powdered activated carbon (PAC) to the aeration basin of an activated sludge treatment plant fed with dye-works waste waters increases the purifying capacity of the plant: removal efficiency rises from 55.8 to 75.6% (COD) and from 78 to 98.5% (BOD₅) and the nitrification-denitrification capacity of the system also increases.The sludge growth parameters and the kinetic constant of biological oxidation were determined on the plant with and without PAC. The addition of PAC decreased overall sludge growth rate and the auto-oxidation factor, but increased the biological removal rate of the substrate by about one order of magnitude.     

活性污泥中原生动物的特征和作用

通过对活性污泥中原生动物的基本生物特征,观察分析方法,在不同环境条件下的种类、数量、活性的表述及其数量和组成的分析,总结出不同种属的原生动物在污水处理过程中的指导作用。     

The activated sludge process—IV: Application of the general kinetic model to anoxic-aerobic digestion of waste activated sludge

This paper discusses the application of the general activated sludge model as set out by Dold et al. (Prog. Wat. Technol.12, 47–77, 1980) and extended by Van Haandel et al. (Wat. Res.15, 1135–1152, 1981), to anoxic-aerobic digestion of waste activated sludge. The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge from which was fed to a number of digesters operated as follows: single reactor flow-through digesters at 4 or 10 days sludge age (retention times) under aerobic or anoxic-aerobic conditions (with 1.5 and 4 h cycle times) and 3-in-series flow-through aerobic digesters each with 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model simulated accurately all the experimental data without the need to change the values of the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate constant in a digester is about two-thirds of that in the secondary anoxic reactor of the single sludge activated sludge system; this allows definition of a fourth denitrification rate constant K₄ for the anoxic-aerobic digester with K₄T = 0.046(1.029)^(T-20) mg(NO₃-N) (mgAVSS d)⁻¹, a constant independent of sludge age. An important consequence of (i) and (ii) above is that the denitrification can be integrated readily into the steady state digester model of Marais and Ekama (Wat. SA2, 163–200, 1976) and used for design purposes.     

类固醇雌激素在活性污泥系统中去除研究进展

类固醇雌激素是内分泌干扰物的一种,具有较强的内分泌干扰性,是水环境中导致内分泌干扰效应的主要物质,对人类的健康存在潜在性危害.污水处理厂是天然水体中雌激素的重要来源之一,目前活性污泥处理工艺在污水处理设施中应用最为广泛.综述了类固醇雌激素的性质、来源及其在活性污泥系统中的去除效果和去除机制,并展望了该领域未来研究发展方向.     

Thickening of waste activated sludge by biological flotation

Waste activated sludge was thickened by biological flotation without polymer flocculant dosage. The BIOFLOT® process utilizes the denitrifying ability of activated sludge bacteria. Gaseous products of anaerobic nitrate reduction cause spontaneous flotation of the sludge suspended solids. Laboratory tests confirmed the dependence of sludge thickening efficiency on available nitrate concentration, flotation time and temperature. Full-scale experiments were performed in a fully automatized unit for discontinuous sludge thickening from wastewater treatment plants with a capacity of up to 5000 I.E. Waste activated sludge from wastewater treatment plants at Pisek. Milevsko and Björnlunda was thickened from 6.2, 10.7 and 3.5 g/l MLSS to 59.4, 59.7 and 66.7 g/t MLSS, respectively. Concentrations of COD, ammonium and phosphate ions were decreased in sludge water. The average nitrate consumption for bioflotation was 21.2 mg NO₁⁻ per 1 g of MLSS of activated sludge. Flotation time ranged from 4 to 48 h.     

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.     

Chemical reaction engineering and activated sludge

The applicability of chemical reaction engineering principles to activated sludge systems is discussed. Based on these principles, an explanation is proposed to the similar performance of plug flow and completely mixed activated sludge systems treating municipal wastewater. The use of batch data for the design of continuous flow reactors is also explained.     

An improved method using respirography for the design of activated sludge aeration systems

For the computation of the oxygen uptake for the aeration tank of the biological treatment plant several methods are available such as the OC/L method, Emde's method with fixed coefficients, Eckenfelder's method, and the method of levels of dissolved oxygen. The method for the determination of oxygen uptake for the treatment of industrial wastewaters was developed. The advantage of this method is a simple calculation of oxygen uptake for industrial biological treatment plant due to independent measurement of oxygen uptake for individual phases. The method is rapid and allows easy determination of individual phases of oxygen uptake.     

Biosorption and dynamics of bacterial populations in activated sludge

Nutritional relations are determining factors in the biological competition between filamentous and floc-forming microorganisms of activated sludge. Biosorption reflects the behaviour of microorganisms in relation to a given substrate. The results obtained from nearly 600 measurements of biosorption carried out in 11 wastewater treatment plants are presented. Biosorption of non-filamentous sludge is less than 30 mg COD/g SS for a 100 mg COD/g SS floc loading. Biosorption increases appreciably with the sludge volume index (SVI). These investigations provide a better understanding of the mechanisms involved in the contact zones. These techniques are successfully experimented in some cases of bulking where biosorption was at least equal to 40 mg COD/g SS.     

Diffusivity, tortuosity and pore structure of activated sludge

This paper describes new techniques in studying and defining pore morphology of activated sludge. Diffusion measurements on activated sludge are carried out in a diffusion cell. The average diffusivity in activated sludge is found to be 7.4 × 10⁻¹⁰ m² s⁻¹. Surface area determinations are used to calculate the mean pore radius of activated sludge flocs. This value is found to be between 108 and 130 Å. The tortuosity of the pores in activated sludge is also calculated and found to have an average value of 2.73.     

Power economy studies on activated sludge treatment

This study was focused on power economy of the activated sludge process which is the most energy consuming stage. The optimisation of oxygen requirements by using a Box complex algorithm method was investigated for different inflow rates, BOD loadings and related operating parameters. Linear regression analysis was used to obtain relationships between oxygen requirement, BOD loading and BOD removal under various operating conditions. The effect of such operating parameters as the MLSS concentration, hydraulic retention time and BOD loading on the power economy was investigated. Organic load and oxygen requirement relations for typical municipal wastewaters are presented in an attempt to obtain power economy in the aeration tank.     

Evolution of microbial communities in the activated sludge process

In a series of bench scale activated sludge experiments, the evolution of sludge microbial communities was studied. The different communities required 2–3 months to reach functional optimum as measured by parameters such as substrate removal efficiency, effluent suspended solids and sludge volume index. Nevertheless, a period of at least 4 months, corresponding to 10 mean cell residence times, was necessary before full nitrification and minimum endogenous respiration were reached. Inoculation with wastewater sludge enhanced the evolvement of the microbial community, but was not essential. Activity parameters such as invertase and ATP-content, as well as the behaviour of the numerically dominant species, suggest that a microbial community evolves to a climax pattern rather than to a distinct type of climax state.     

活性污泥数学模型ASM1在工程设计中的应用(下)

对于活性污泥数学模型(ASM1)在污水处理生物反应器设计上的应用方法进行了探讨，并列举设计实例对应用方法作了介绍，以指导试验研究、工程设计或运行管理。     

Effects of bacterial activity on estrogen removal in nitrifying activated sludge

The effects of bacterial activity on the degradation of estrone (E1), estradiol (E2), estriol (E3) and ethinylestradiol (EE2) in nitrifying activated sludge (NAS) were studied with different substrates and organic loading rates (OLRs) and low temperature conditions. Heterotroph was shown to have utilized glucose prior to E1 for metabolism. The co-metabolism of ammonia oxidizing bacteria (AOB) dominated the degradation of E1, E2 and EE2 in NAS. The higher the organic loading, the higher the rate of organic matter transformation, with less ammonia oxidation and less degradation of E1, E2 and EE2. The degradation of E3 in NAS was shown to be largely due to heterotroph metabolism. On the basis of the difference of apparent activity between heterotroph and AOB at 4 degrees C, the process of estrogen degradation via the co-metabolism of AOB was able to be identified.     

Control of activated sludge settleability using preaeration and preprecipitation

This paper deals with the addition of a preaeration and a preprecipitation stage to a conventional activated sludge process. The experiments were carried out in a pilot plant using wastewater from the city of Valencia (Spain) as feed. The effect of the F/M ratio and sludge age on sludge settleability was established. In both cases, process stability was observed to increase with respect to the conventional process. Good sludge settleability was thus assured in a greater F/M ratio range. A comparative economic study was also carried out.     

Stroboscopic determination of settling velocity, size and porosity of activated sludge flocs

A multi-exposure photographic method was developed for the combined measurement of the settling velocity and size of activated sludge flocs. The proposed method mainly differs from the previous stroboscopic tests by introducing a new experimental arrangement which ensures sharp images of flocs on photographs.The relationships between individual floc-settling velocity and the floc size were found to be linear or fractional power functions. All these relationships were well correlated.Based on a simplified floc structure assumption and results of experimental measurements of floc-settling velocity and size, the floc porosity was determined. The porosity increased at two distinct rates as the floc size increased.