Some practical aspects of the “biocarbon process”

In the presence of granular activated carbon the aerobic decomposition of organic compounds is facilitated (Koppe et al., 1974a,b). As could be shown by many laboratory tests several effects are given. First of all the faster adaptation of the bacteria has to be mentioned which is most important with substances which are difficult to be degraded like pentaerythrite. Additionally the degradation efficiency of the activated sludge process will be increased and equalized by granular activated carbon. Finally the effect of low temperatures can be compensated by the presence of granular activated carbon. With domestic wastewater for instance full nitrification could be obtained at a temperature of 4°C.Adsorption of organic compounds cannot be the explanation because the effect could be observed during several months whereas the calculated adsorption capacity had to be exhausted after two days. True causes are that specialized bacteria are retained in the pores and niches of the activated carbon in the lag-phase, that micro-organisms find area to grow in the log-phase (approximately 100 m²/m³ with 1 kg m⁻³ granular activated carbon) and that the enrichment of some exoenzymes at the activated carbon occurs (compare Figs. 1 and 2; and Müller & Sekoulov, 1975; Lue-Hing et al., 1976; Larsson et al., 1976; Rincke & Wolters, 1970). Since micro-organisms and activated carbon intimately react, this modification of the activated sludge process was called “biocarbon process” which has to be distinguished from the process with powdered activated carbon (de Walle & Chian, 1977).After completion of the laboratory tests, full-scale tests were started. In full-scale tests several difficulties had to be overcome. In some cases it was difficult to avoid the sedimentation of the granular activated carbon in the aeration tanks. Another task was the separation of the carbon from the surplus activated sludge. Finally it was of interest to determine how much carbon is lost by wet abrasion to be able to make a feasibility calculation. The full-scale tests have been performed in two wastewater treatment plants of the Ruhrverband: Nordenau and Günne.     

Revue des reactions des algues aux micropolluants mineraux et organiques; consequences ecologiques et possibilites d'applications industriellesAlgae reactions to mineral and organic micropollutants, ecological consequences and possibilities for industrial-scale application: a review

An aquatic ecosystem may react to pollution in different ways, some of which combat the pollution actively; in particular, algae participate therein by developing various substances capable of complexing or degrading numerous organic or mineral pollutants.When heavy metals are not directly accumulated in algae, they can often be complexed by their extracellular metabolites (Hart, 1981), e.g. hydroxamates (McKnight and Morel, 1980; Jardim and Pearson, 1984), to form organo-metallic compounds; the ecological consequences of these phenomena, most often due to the presence of Cyanophyceae (Walsby, 1974), are varied:Useful effects: greater assimilability of certain indispensable trace elements (Provasoli et al., 1957; Johnston, 1964; Allen, 1976; Murphy et al., 1976; Gaechter et al., 1978), reduced toxicity of heavy metals brought in by pollution (Barber, 1973), etc.;Harmful effects: among others, antagonistic action against copper-based algaecidal treatments (Gaechter et al., 1978; Gnassia-Barelli et al., 1978; Van den Berg et al., 1979; McKnight and Morel, 1980).Organic micropollutants are often metabolized or even assimilated by algae, for instance:Hydrocarbons: assimilation by marine algae such as the diatom Chaetoceros calcitrans (Boutry et al., 1977a, b), or by fresh water algae (Krauss et al., 1973; Schroeder and Rehm, 1981a, b);Phenols: metabolization which can go as far as to completely remove them (Werner and Pawlitz, 1978; Stom et al., 1978), through the action of phenoloxidases which induce the formation of transient degradation products, in particular quinones (Stom et al., 1978);Pesticides: these more stable compounds are most often accumulated in algae (Soedergren, 1968; Vance and Drummond, 1969); however, certain algae are capable of causing their partial degradation (Miyazaki and Thorsteinson, 1972; Neudorf and Khan, 1975; Werner and Moerschel, 1978; Goulding and Ellis, 1981), but this may result in the temporary appearance of metabolites more toxic than the initial product (e.g. DDE from DDT);PCBs: these still more stable micropollutants are fixed, without being metabolized, by living algae (Keil et al., 1971; Veber, 1980), and even dead ones (Urey et al., 1976).The various reactions we have just seen above explain that in nature, certain algae prove specifically tolerant to various industrial wastes that contain mineral pollutants (Madgwick and Ralph, 1977; Say et al., 1977; Palmer, 1980; Strong et al., 1982), or organic pollutants (Palmer, 1980; Walsh et al., 1982).These observations, made both in the laboratory and in the field, could well lead to new applications in the biological treatment of industrial waste water; such possibilities have already been proved for vascular plants, for instance for the removal of heavy metals (Wolverton, 1975a, b and c; Tridech et al., 1981; Muramoto and Oki, 1983) or phenols (Seidel, 1965; Seidel and Kickut, 1967; Karaseva and Papchenkov, 1974; Kaminskii and Gvozdeva, 1976; Stom et al., 1978). The new generation of biological treatments of industrial effluents will be based on selected algae species acting in symbiosis with bacteria (Yurovskaya et al., 1968; Bagnyuk et al., 1975) in traditional lagooning or through more intensive processes, e.g. “activated algae” (McGriff and McKinney, 1971; McKinney et al., 1971) or cultures of algae immobilized in agar beads (Pore and Sorenson, 1981) or on rotating discs (Przytocka-Jusiak et al., 1984b), etc.Where the latter are still in the pilot plant stage, natural lagooning is now a tried-and-tested technique which has already been applied to certain industrial effluents (Lee et al., 1978; Palmer, 1980; Rebattu, 1981; Altona et al., 1983), but without previous selection of the species of algae to be used: they will be selected as a function of their ability to remove pollutants: either by bioaccumulation as for heavy metals (Filip et al., 1979; Shumate et al., 1980; Nakajima et al., 1981; Becker, 1983) or pesticides or else by metabolization and/or assimilation as for phenols (Stom et al., 1978), nitrogen-laden effluents (Matusiak et al., 1976, 1977; Przytocka-Jusiak et al., 1984a, b), hydrocarbons, etc.In addition, it should be pointed out that in its conventional applications, natural lagooning often suffered from the lack of additional clarification of the effluent; the latter may contain over 100 mg 1⁻¹ of residual algae (Shelef et al., 1972; Bratby and Marais, 1974; Harris et al., 1977; Russell et al., 1983; Przytocka-Jusiak et al., 1984a), which then bring in a high additional BOD₅, especially after their death (Varma and Digiano, 1968; King et al., 1970; Rance Bare et al., 1975; Friedman et al., 1977; McGimpsey, 1978). Therefore, it is always more advisable to remove the algae and possibly use them as a source of energy or food.In the cases studies here, this additional treatment would be absolutely essential to protect the receiving water not only from the algae themselves, but also from the micropollutants that they would have accumulated. The different processes available for harvesting algae are listed: filtration through sand (Harris et al., 1977; Filip et al., 1979; Russell et al., 1983), microstraining (Kormanik and Cravens, 1978 and 1979; Cravens and Lauritch, 1982; Harrelson and Cravens, 1982), dissolved air flotation (Van Vuuren et al., 1965; Funk et al., 1968; Bratby and Marais, 1974; Rance Bare et al., 1975; Stone et al., 1975; Shelef, 1982; Viviers and Briers, 1982), sedimentation (Friedman et al., 1977), separation through microfiltration or ultrafiltration membranes (Shelef et al., 1972; Castelas et al., 1984), etc.In fact, there is not one system which is universally applicable: this explains the wide-ranging opinions on the subject. Depending on the case, microstraining, direct filtration, accelerated settling with sludge contact, membrane technology and above all dissolved air flotation may well be usefully applied in this field. The performances of the various processes are examined, and several principles for the choice of a method of separation of algae as a function of local conditions are proposed.     

Anaerobic treatment of wastes containing methanol and higher alcohols

Experiments have been performed to ascertain the feasibility of anaerobic digestion for the treatment of an alcoholic waste (i.e. fusel oil), consisting of approx. 50% methanol and 50% higher alcohols. Batch experiments as well as continuous experiments have been conducted. The continuous experiments have been carried out using the “Upflow Anaerobic Sludge Blanket” (UASB-) process. As inoculum a sugar beet waste grown and highly settleable and active anaerobic sludge (SBA-sludge) has been used. The SBA-sludge was shown to be superior to digested sewage sludge as seed material for an anaerobic treatment process, because—although it in fact is adapted to the fermentation of volatile fatty acids (VFA)—it does not have any significant difficulty with respect to the methanogenesis of the alcohols present in the fusel oil waste. The breakdown of higher alcohols starts immediately and that of methanol within a few days, depending on the initial load applied. In the UASB-experiments sludge loads up to 0.6 kg COD·kg VSS⁻¹·day⁻¹ could already be well accommodated within 1 week, so that within this period a space load could be handled as high as 20 kg COD·m⁻³·day⁻¹, simply by supplying the reactor with approx. 30 kg SBA-VSS·m⁻³ averaged over the total reactor volume.Contrary to recent findings of Smith & Mah (Appl. envir. Microbial. 36, 870–879, 1978), which were obtained with a pure culture of Methanosarcina barkeri, the sludge is capable of fermenting VFA and methanol rapidly and simultaneously, provided the conditions for VFA and methanol fermentation are favourable. However, as in previous experiments with aqueous solutions of methanol (Lettinga et al., Water Res. 13, 725–737, 1979), we observed that the digestion process can easily become upset, especially with respect to the degradation of VFA. Once again indications have been obtained that one or more trace elements are of eminent importance with respect to the stability of the process. At present the operation of a stable anaerobic treatment process for methanolic wastes cannot be guaranteed.     

The adsorption of bovine serum albumin by activated sludge

The rapid removal, from suspension, of between 2–% of bovine serum albumin (BSA) by BSA acclimated activated sludge was attributed to adsorption. The extent of adsorption varied with the substrate to biomass (s/b) ratio. The concentration of BSA adsorped was influenced by both the concentration of BSA and the concentration of activated sludge. The experimental data did not conform to the calssical adsorption equations of Langmuir (J. Am. chem. Soc.40, 1361–1403, 918) or Freundlich (Colloid and Capillary Chemistry, Methuen, London, 1926) but to a newly developed equation, the activated sludge adsorption equation (ASAE). This new equation was tested and proven by experimental data and by data obtained independently by Banerji et al. (J. Wat. Pollut. Control Fed.40, 161–173, 1968) who investigated starch removal by activated sludge. Following the development of the ASAE, it was found possible to express both the concentration of BSA adsorbed per unit weight activated sludge (m) and the concentration of BSA in equilibrium per unit weight activated sludge (C/b) as a function of the concentration of BSA added to the system per unit weight adsorbent (C_t). Thus adsorption could be expressed as a function of the substrate to biomass (s/b) ratio.     

Removal of metals and fate of N and P in the bacterial leaching of aerobically digested sewage sludge

The solubilization of metals from aerobically digested sewage sludge was performed biologically using Thiobacillus ferrooxidans, in a continuously stirred tank reactor (CSTR). Experiments involved the preacidification of the sludge to pH 4.0 and the addition of 4 g FeSO₄-7H₂O per liter of sludge. Reactors were operated with 20 g/l total solids (2% TS), 0.5 volume of air per reactor volume per minute, agitation at 300 rpm and a 20% recirculation rate. A minimal mean hydraulic residence time (t) of 0.75 day, one half the time required in a batch system, resulted in solubilization of 52% of the Cu, 62% of the Zn and 78% of the Mn. The leached sludge was more easily dewatered than untreated sludge, and would not likely require the addition of polymer if a plate filter press were used. Metals did not reprecipitate during filtration. A small quantity of added lime was sufficient to precipitate the metals; selective precipitation could permit the separation of ferric hydroxide from valuable metals (Cu, Zn, Ni, Cd), which may then be recovered. No significant changes in the total nitrogen and phosphorus content occurred during solubilization. Biological solubilization produced a better quality sludge for agriculture, as well as avoiding the dispersal of metals into the environment.     

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.     

Parametric stress distribution in shell-of-revolution sludge digesters of parabolic ogival form

Egg-shaped sludge digesters have become popular in relatively recent times owing to their superior functional performance and lower maintenance costs in comparison with conventional cylindrical digesters. These innovative structures are usually constructed as thin shells of revolution in concrete, designed to withstand principally the hydrostatic pressure loading from the contained liquid. As regards the precise shape of the egg shell, a number of mathematical shell surfaces may be envisaged, and the stress distribution will very much depend on the chosen form. In this paper, it is desired to explore the possible adoption of the parabolic ogival shell as a sludge digester. The stress distribution in such a shell is expressed in terms of a single governing parameter ξ, greatly facilitating the investigation. For various values of ξ covering the most practical range for egg-shaped digester shells, recommendations are made regarding the positioning of supports. Taking into account maximisation of tank capacity, minimisation of peak stress resultants in the shell, and ease of prestressing, the best range of ξ for parabolic ogival digester shells is identified. The overall conclusion is that from a structural and functional point of view, the parabolic ogival profile is suitable for adoption in the design of egg-shaped concrete sludge-digester shells.     

Potential for parasitic disease transmission with land application of sewage plant effluents and sludges

Land application of sewage plant effluents and sludges is being considered by planners because of environmental problems arising from alternative approaches and as a means of recovering the soil enrichment qualities of sewage effluents and sludges. A review of the literature shows that primary and secondary treatment, anaerobic sludge digestion, and routine disinfection (chlorine or ozone) do not destroy completely parasitic forms. Because of their weight most cysts and eggs are found in the sludge. Sludge digestion does destroy protozoan cysts but not all metazoan eggs. These cysts and eggs are extremely resistant in field conditions and some can persist infective for long periods. Documented disease transmission to humans from land application programs is related only to use of raw, not treated, sewage on land. Some animal disease transmission has been found related to untreated and partially treated sewage. Those who have examined sewage plant effluents and sludges for parasitic cysts and eggs have found them present. The most commonly reported species are: E. histolytica, Ascaris lumbricoides, Trichuris trichiura, Hymenolepis spp, Taenia sp. Enteroblus vermicularis, Ancylostoma and Necator. Destruction of all pathogenic forms can be assured by adequate heating of material to pasteurization temperatures of 60°C or more for 30+ min. Direct heating or composting can accomplish this. Parasitic disease transmission can be reduced by controlling the types of land to which these sewage plant products are applied. Parasitic disease transmission should be considered in developing the technology and/or management approaches to land application of sewage plant products for soil enrichment purposes.     

Effects of stabilizers on CO2 fixation capacity in neutralization of alkali construction sludge

Construction sludge, generated from tunneling and piling, is typically in a liquid state. It can be improved via physical treatments, such as dehydration, and/or chemical treatments, using stabilizers, in order to to be recycled as construction material. To adjust the strength of sludge, chemical treatments are often preferred. However, chemical treatments frequently result in alkali leaching. Methods to reduce alkalinity by curing the alkaline sludge under CO₂ gas at a certain concentration have been proposed in Japan. In recent years, technologies that utilize CO₂ to improve the quality of cementitious material have received considerable attention in terms of carbon capture. Therefore, the effects of stabilizers on the CO₂ fixation capacity of alkaline sludge during pH neutralization were investigated in this study. Accelerated carbonation and carbonate content measurement tests were conducted to detect the CO₂ content fixed in alkaline sludge specimens treated with various stabilizers. The test results showed that the fixed maximum CO₂ content per gram of dry mass of sludge, (m_CO2)^max, increased with the calcium oxide (CaO) content of the stabilizer(s) per gram of dry sludge, C_CaO. However, the rate of increase in (m_CO2)^max with C_CaO was significantly affected by the type of stabilizer used. In the case of quicklime (QL), the ratio of (m_CO2)^max to C_CaO was approximately 0.5, whereas, in the cases of fly ash (FA) and steel slag (SS), the ratio was approximately 0.25. The ratios for biomass ash and paper sludge ash were between that for QL and that for FA and SS. Detailed analyses of the test results suggest that the CaO content per gram of stabilizer(s) in the sludge, C*_CaO, can provide an estimate of the fixed maximum amount of CO₂ per gram of stabilizer(s) in the sludge, (m*_CO2)^max. However, other factors, including the amount of water-soluble Ca, should be considered for a precise evaluation. Additionally, the experimental results showed that the decrease in pH owing to neutralization increases with the increasing C_CaO. However, the type of stabilizer did not significantly affect the relationship between the degree of CO₂ fixation and the degree of neutralization.     

Sewage sludge conditioning by Fe(II)‐activated persulphate oxidation combined with skeleton builders for enhancing dewaterability

In this study, a joint application of Fe(II)‐activated persulphate oxidation and skeleton builders is used to condition sewage sludge for subsequent dewatering. The study mainly focuses on their efficacies and the optimization of the major operational parameters. The experimental results show that the joint application for conditioning sewage sludge is effective, especially using lime and ordinary Portland cement (OPC) as skeleton builders. Additionally, it is revealed that Fe(II)‐activated persulphate oxidation needs sufficient reaction time (20 min) to degrade organics in the sludge. The optimal conditions of this process are at Fe²⁺ = 47.6 mg g^?1 (dry solids), S₂ = 119.1 mg g^?1, lime = 446.4 mg g^?1, and OPC = 297.6 mg g^?1, under which the water content of dewatered sludge cake is 54.8% and the specific resistance to filtration (SRF) is 4.3 × 10¹¹ m kg^?1 with a reduction efficiency of 96.6%.     

The mechanical behaviour of synthetic sandstone with varying brittle cement content

The purpose of this work was to investigate the influence of cement on the mechanical behaviour of granular rocks. Following the technique described in den Brok et al. [den Brok, S. W. J., David, C. and Bernabé, Y., Preparation of synthetic sandstones with variable cementation for studying the physical properties of granular rocks. C. R. Acad. Sci., 1997, 325, 487–492], two blocks of synthetic sandstones with different cement content were prepared for mechanical testing under hydrostatic and triaxial conditions. The results of the mechanical tests show that the behaviour of the synthetic rocks compares well with that of natural sandstones. Increasing the amount of cement from 3 to 5% in volume had important consequences on the mechanical properties: the critical pressure, strength and elastic moduli were significantly increased and the brittle-to-ductile transition was shifted towards higher pressures. We compared our results to the models of Zhang et al. [Zhang, J., Wong, T. -F. and Davis, D. M., Micromechanics of pressure-induced grain crushing in porous rocks. J. Geophys. Res., 1990, 95, 341–352] and Wong et al. [Wong, T. -F., David, C. and Zhu, W., The transition from brittle faulting to cataclastic flow in porous sandstones: Mechanical deformation. J. Geophys. Res., 1997, 102, 3009–3025]. We conclude that Zhang et al.'s microstructural parameter φD (i.e. the product of porosity φ by grain size D) appeared to be a scaling parameter for both the failure envelopes and the critical pressure as defined in these models. Intuitively, the contact length L is expected to play a crucial role in the mechanical properties of granular materials. Accordingly, we made a statistical analysis of this microstructural parameter in our synthetic materials and in a suite of natural sandstones. A positive correlation with Young's modulus and a negative correlation with porosity were found. This last result gives a physical background for the use of parameter (φD) in theoretical models. We want to emphasize that working on synthetic sandstones allows for a better control of the structural parameters (grain size, sorting, cement content, etc.) which appear to be so important for the mechanical properties of granular rocks.     

Influence of secondary settling tank performance on suspended solids mass balance in activated sludge systems

Secondary settling is the final step of the activated sludge-based biological waste water treatment. Secondary settling tanks (SSTs) are therefore an essential unit of producing a clear effluent. A further important function of SSTs is the sufficient thickening to achieve highly concentrated return sludge and biomass within the biological reactor. In addition, the storage of activated sludge is also needed in case of peak flow events (Ekama et al., 1997). Due to the importance of a high SST performance the problem has long been investigated ( [Larsen, 1977], [Krebs, 1991], [Takács et?al., 1991], [Ekama et?al., 1997], [Freimann, 1999], [Patziger et?al., 2005] and [Bürger et?al., 2011]), however, a lot of questions are still to solve regarding e.g. the geometrical features (inflow, outflow) and operations (return sludge control, scraper mechanism, allowable maximum values of surface overflow rates). In our study we focused on SSTs under dynamic load considering both the overall unsteady behaviour and the features around the peaks, investigating the effect of various sludge return strategies as well as the inlet geometry on SST performance. The main research tool was a FLUENT-based novel mass transport model consisting of two modules, a 2D axisymmetric SST model and a mixed reactor model of the biological reactor (BR). The model was calibrated and verified against detailed measurements of flow and concentration patterns, sludge settling, accompanied with continuous on-line measurement of in- and outflow as well as returned flow rates of total suspended solids (TSS) and water.As to the inlet arrangement a reasonable modification of the geometry could result in the suppression of the large scale flow structures of the sludge-water interface thus providing a significant improvement in the SST performance. Furthermore, a critical value of the overflow rate (q_crit) was found at which a pronounced large scale circulation pattern develops in the vertical plane, the density current in such a way hitting the outer wall of the SST, turning then to the vertical direction accompanied with significant flow velocities. This phenomenon strengthens with the hydraulic load and can entrain part of the sludge thus resulting in unfavourable turbid effluent.As a representative case study an operating circular SST most commonly used in practice was investigated. Focusing on the sludge return strategies, it was found that up to a threshold peak flow rate the most efficient way is to keep the return sludge flow rate constant, at 0.4Q_MAX. However, once the inflow rate exceeds the threshold value the return sludge flow rate should be slowly increased up to 0.6Q_MAX, performed in a delayed manner, about 20-30 min after the threshold value is exceeded. For preserving the methodology outlined in the present paper, other types of SSTs, however, need further individual investigations.     

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.     

Effluent quality variation from multicomponent substrates in the activated sludge process

The objectives of this investigation were: (1) to examine the overall substrate removal of a three component mixture by an acclimated seed using total organic carbon measurements, (2) to observe the rates of removal of each of the three components in the mixture at four different food-to-microorganism ratios (F/M), (3) to show the effects of the composition of the substrate with varying degradability on effluent quality, and (4) to observe the effects of sludge age on total substrate removal.To accomplish these objectives, sludge from a municipal sewage treatment plant was acclimated as seed in a continuous flow, completely mixed laboratory reactor. A multicomponent substrate consisting of a mixture of glucose, phenol and sulfanilic acid, was fed at different F/M ratios. The removal rate was determined as total organic carbon and specific analytical measurements for each substrate in the influent and effluent samples were also made. Various combinations of glucose, phenol and sulfanilic acid were used as a substrate in three runs. This made it possible to observe the removal rate of each substrate in the mixture as related to their individual biodegradability as well as their influent concentrations.The results showed that for the three substrates employed in this study, the overall removal rate, in terms of total organic carbon in a mixed acclimated culture, is the sum of the individual specific removal rates. The effluent quality in terms of soluble TOC was related to the F/M or to the sludge age using Eckenfelder's kinetic model.     

Comparative disinfection of treated sewage with chlorine and ozone: Effect of nitrification

Chlorine and ozone were compared in pilot plants (capacity about 3.2 m³ h⁻¹), which were fed with the same activated sludge treated and filtered water. Together with physico-chemical analysis the water was analysed for different types of microorganisms, including vegetative bacteria (total and thermotolerant coliforms, faecal streptococci and Pseudomonas aeruginosa), bacterial spores (spores of aerobic bacteria at 37°C and sulphite reducing clostridia) and bacterial viruses (somatic coliphages and F-specific bacteriophages).The average chlorine and ozone dose were, respectively, 3.65 and 15.3 mg l⁻¹ of water, while after a contact time for both of about 25 min the average residual concentrations were 1.79 and 0.35 mg l⁻¹ of water. These residuals were measured with the DPD-method. The ammonia-N concentration varied greatly (0.06–72.0 mg l⁻¹) and was used to group the data into four classes: (1) non-nitrified water, defined as water in which nitrate-N was smaller than ammonia-N; (2) moderately nitrified water, in which nitrate-N was larger than ammonia-N and the ammonia-N was higher than 2 mg l⁻¹; (3) well nitrified water, defined as water in which ammonia-N was lower than 2 mg l⁻¹; (4) very well nitrified water, in which ammonia-N was smaller than 0.5 mg l⁻¹.This classification indicated that the concentrations of most other impurities decreased with a better nitrification. Statistical analysis of the data showed also that ozone was a better disinfectant than chlorine in the case where the disinfection is based upon their residual content. The degree of nitrification had a greater effect on chlorine disinfection than on ozone disinfection.During chlorination the total residual chlorine decreased, with better nitrification; the chlorine demand increased; the composition of the residual chlorine changed very much and the inactivation of bacterial viruses improved. The vegetative bacteria showed a varying pattern; most were inactivated in moderately nitrified water, when the dichloramine concentration was highest and false positive FAC concentration was lowest of the four classes. Reduction of bacterial spores was not observed.During ozonization other effects were indicated. Reductions of most organims increased slightly with better nitrification; only reductions of F-specific bacteriophages decreased. There was also a small decrease of bacterial spores. The treated effluent had a high ozone consumption and the inactivation of the organisms was low in relation to ozone dose and residual ozone.The bromide concentration (0.3–2.9 mg l⁻¹) effected the chemistry of chlorine and ozone and had a positive effect on chlorine and ozone disinfection of total coliforms.For most types of micoorganisms the disinfection coefficients of the Selleck model and the germicidal efficiencies could be determined.     

Concentration du virus de l'hepatite a sur des membranes de cellulose

Viral hepatitis type A is the most prevalent waterborne disease in U.S.A. and the number of cases has been increasing in recent years (Melnick et al., 1978). Till now, few works were performed on Hepatitis A Virus (HAV) concentration in water (Hejkal et al., 1982, Elkana et al., 1983). In this paper the filter adsorption-elution method, widely used with other viruses (Wallis and Melnick, 1967; Fields et Metcalf, 1975; Smith and Gerba, 1982), was selected to concentrate HAV from experimentally-contaminated distilled water. Filtration was performed through two cellulose membranes (RAWP 04700 and HAWP 04700 Millipore). Eluate or filtrate viruses were precipitated by polyethylene glycol 6000. HAV is detected by solid phase radioimmunoassay according to a previously described method (Deloince et al., 1982). Figure 1 shows the results of adsorbing HAV at different pH levels. Analysis of variance pointed out that, for the pH levels between 3 and 4, the differences were not significant (P = 0.05). Table 1 shows the effects of pH and number of passages of 3% beef extract or 0.2 M glycin buffer on HAV elution. For both eluents the differences in function of pH levels and number of passages of eluent through the membrane were not significant (variance analysis P = 0.05). On the other hand, the comparison between the two eluents pointed out the higher efficiency of beef extract (t-test, P = 0.001). After this procedure, HAV replication occurred in human hepatocarcinoma cells PLC/PRF/5 (Fig. 2) inoculated according to a previously described method (Crance et al., 1983). As poliovirus (Sobsey et al., 1973), HAV adsorption is the most efficient at acid pH levels. Between pH 4.5 and 5, the remarkable adsorption decrease might be related to the inversion of the HAV electrostatic charges sign, i.e. to the occurrence of an isoelectric point. The HAV elution is different from the poliovirus one, the efficiency of which increased with pH (Wallis et al., 1972) and eluent passage numbers (Farrah et al., 1976). That might suggest that from pH 7.5, both the HAV particles and membranes have negative charges which give enough repulsive forces to allow a good elution efficiency. Improvement of HAV elution efficiency by beef extract is similar to a result obtained with poliovirus by Landry et al. (1978). This effect might be explained by the proteinous material presence in beef extract. HAV replication in cell cultures shows the biological properties preservation after this procedure.     

Biological treatability of dairy wastewaters

Biological treatability of an integrated dairy plant wastewater containing a small fraction of whey-washwaters mixture has been experimentally investigated. Emphasis has been placed on the assessment of the initially inert fraction, S₁ and soluble residual microbial products, S_p. Parallel batch experiments have been conducted to determine the kinetic and stoichiometric coefficients of the degradable COD. The results have shown that the wastewater tested had practically no initially inert fraction, but generated residual microbial products amounting to 6–7% of the initial degradable COD. The results obtained have been fed into a set of equations describing the steady state operation of an activated sludge system with sludge recycle and a relationship indicating the variation of the total effluent COD with the sludge age has been defined for the wastewater tested. It is noted that effluent COD cannot be biologically reduced below 85 mg l⁻¹, regardless of the sludge age, due to generation of residual fractions.     

Combined permeable pavement and photocatalytic titanium dioxide oxidation system for urban run‐off treatment and disinfection

Permeable pavement systems (PPS) are frequently associated with high removal efficiencies for water quality parameters. Their effluent can, therefore, be recycled, for example, for sprinkling onto gardens. Nevertheless, some stakeholders fear that potentially pathogenic organisms within the treated run‐off could be too high, and therefore they request disinfection before recycling. The aim of this paper is, therefore, to assess the efficiency of a batch flow combined titanium dioxide (TiO₂) and ultraviolet (UV) light photocatalytic reactor in removing water‐borne microbial contaminants from the effluent of PPS. Combined TiO₂ and UV photocatalytic reaction times between 80 and 100 min were required for the complete removal of Escherichia coli, total coliforms and faecal Streptococci, which had mean initial counts of 1.5 × 10⁷, 4.4 × 10⁶ and 6.9 × 10⁵ colony‐forming units (CFU) per 100 mL, respectively. In comparison, UV disinfection alone resulted in insignificant microbial removal. Suspended TiO₂ powder was more effective than small immobilised TiO₂ crystals.     

Investigation of bacterial community in activated sludge with an anaerobic side-stream reactor (ASSR) to decrease the generation of excess sludge

The goal of this study was to investigate the bacterial community in activated sludge with an anaerobic side-stream reactor (ASSR), a process permitting significant decrease in sludge production during wastewater treatment. The study operated five activated sludge systems with different sludge treatment schemes serving as various controls for the activated sludge with ASSR. Bacterial communities were analyzed by denaturing gradient gel electrophoresis (DGGE), sequencing and construction of phylogenetic relationships of the identified bacteria. The DGGE data showed that activated sludge incorporating ASSR contained higher diversity of bacteria, resulting from long solids retention time and recirculation of sludge under aerobic and anaerobic conditions. The similarity of DGGE profiles between ASSR and separate anaerobic digester (control) was high indicating that ASSR is primarily related to conventional anaerobic digesters. Nevertheless, there was also unique bacteria community appearing in ASSR. Interestingly, sludge in the main system and in ASSR showed considerably different bacterial composition indicating that ASSR allowed enriching its own bacterial community different than that from the aeration basin, although two reactors were connected via sludge recirculation. In activated sludge with ASSR, sequences represented by predominant DGGE bands were affiliated with Proteobacteria. The remaining groups were composed of Spirochaetes, Clostridiales, Chloroflexi, and Actinobacteria. Their putative role in the activated sludge with ASSR is also discussed in this study.     

Compaction of flocculated material

The device used in the experiment consists of a flat-bottomed graduated cylinder and a coaxial plunger. A suspension flocculated with chemicals is sedimented after being mechanically worked within the graduate, and the supernatant water is removed with a pipette. The plunger is thrust into the sludge at a constant speed. The sludge is not only compressed but also flows into the annular gap between the plunger and the graduate, resulting in liberation of water. The liberated water is accumulated on the sludge in the annular gap. The “sludge bulkiness” β is used to describe the volumetric proportion of sludge and solids in it. The sludge bulkiness values before and after the “plunger test” are denoted as β_i and β_f, respectively. The values of β_i and β_j have been explored as a function of the time of the mechanical working. As a result, there is a definite time lag between the maximum value of β_i and the minimum value of β_f. The minimum value of β_j is obtained when the sludge consists of “pelleted flocs”.