Oxygen uptake rates for determining microbial activity and application

The method presented involves using the oxygen uptake rates of activated sludges for determining the microbial activity and viability. The microbial activity correlates well with the substrate reduction first order rate constant. K₁, determined in batch operations, and with the specific substrate utilization rate, q, of steady state operations. The microbial viability determined based on respiratory activity would result in slightly higher values than other means such as plate counting, since some of the respiratory activity is contributed by nonviable yet active cells. The extent of respiratory activity attributed to the nonviable cells increases as the biological solids retention time increases (or net growth rate decreases). Since the loss of ability of multiplication is not necessarily associated with loss of biochemical activity, the viability determined by the respiratory activity would represent more realistically the activity of microbes and thus is suggested as the preferred technique.     

A method for determining specific surface area of activated sludge by dye adsorption

A new technique is discussed for measuring the surface area of activated sludge. The method is shown to be easy to perform and reproduceable. The results indicate that activated sludge is highly porous with a specific surface area of between 40–140 m² g⁻¹ dry solids.     

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.     

Microbial activity in aerobic sludge digestion

Laboratory experiments were performed to study variations in microbial activity during aerobic sludge digestion. The main objective was a critical evaluation of the most common measures of activity, these being: ATP, plate counts, dissolved oxygen uptake rate and activity of dehydrogenase enzymes. Their variation with digestion time was monitored for batch and semi-continuous flow regimes at three different operating temperatures: 10, 20 and 30°C. The relation between these measures and the mass content of the sludge was also investigated.It was found that ATP offers the best estimate of activity, while plate counts can result in erroneous and misleading interpretations of the metabolic state of the mixed liquor population. ATP was found to parallel the decrease in biodegradable suspended solids (BVSS) during batch digestion, when corrected for solids reductions from cell lysis. It was concluded that the decrease in ATP does reflect a decrease in active biomass from the endogenous metabolism of the bacterial population, and that the ATP content per active cell mass remains constant with detention time thus allowing the estimation of active fraction of the sludge.     

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.     

A rapid method for determining the toxicity of chemicals to activated sludge

This paper reports the development of a method to determine the toxicity of chemicals to activated sludge. In the method, activated sludge was exposed to various concentrations of test chemicals and the inhibition of [¹⁴C]glucose uptake was measured after 15 min. Data for the decrease in glucose uptake as a function of the log of the test chemical concentration was analyzed by a nonlinear regression model to determine the concentration of chemical inhibiting uptake by 50% (IC₅₀ value). In control experiments, glucose uptake in the absence of test chemicals was rapid, specific and totally dependent on the presence of metabolically-active activated sludge. However, uptake in the presence of inorganic and organic test chemicals showed significant, dose-dependent decreases as the concentration of test material increased. Inhibition of uptake was accurately described by the nonlinear regression model, and calculated IC₅₀ values for two chemicals, mercuric chloride and 3,5-dichlorophenol, agreed well with values reported in the literature to adversely affect wastewater treatment plant operation. Based on the results of our studies, inhibition of glucose uptake proved to be a rapid, accurate and reproducible method of determining the toxicity of chemicals to activated sludge.     

A rapid method to quantify nitrifiers in activated sludge

Quantification of bacteria using Fluorescence In Situ Hybridization (FISH), confocal laser scanning microscopy (CLSM) and image analysis is very time consuming and requires the availability of an expensive microscope. Therefore, a rapid method to quantify nitrifying bacteria in activated sludge using FISH and epifluorescence microscopy was developed. The quantification of the biovolume is based on manual counting of the aggregates formed by nitrifying bacteria and determination of their size. The overall uncertainty of the method was evaluated as a function of the number of analyzed microscopic fields. It was found that 10-15 microscopic fields for ammonia-oxidizing bacteria and 6-8 microscopic fields for nitrite-oxidizing bacteria per sample were optimal regarding effort and accuracy. Accordingly, the time needed for one sample was only 5-15 min, compared to about 1h for the quantification with CLSM and image analysis. As a consequence, this method also allows for the measurement of extended time series with a reasonable effort. The comparison of the determined biovolume and the measured activity showed an explicit correlation.     

活性污泥法处理污水的原理及影响因素

阐述了微生物氧化、分解污水中有机物的原理 ,并分析了该过程中的影响因素及运行过程中常见的问题 ,对推广污水的生化处理具有一定的参考意义。     

A practical procedure for the microbiological monitoring of activated sludge plant functioning

The activated sludge process is one of the most used procedures for removing organic materials and nutrients from wastewater. In this article, microbiological monitoring was applied to supervise the functioning of an activated sludge plant. Samples were taken weekly at three points: aeration tank, returned sludge and effluent. Identification of four functional groups of microorganisms, Gram‐positive and Gram‐negative bacteria, protozoa, metazoa and algae in fresh specimen investigation were used to assess the performance of the plant. The results revealed that initially there were undesirable microorganisms in the aeration tank and in the returned sludge. The density of these organisms was reduced and replaced by Gram‐negative bacteria, ciliates, rotifers and nematodes, which was an indication of stabilization. The microbiological analysis using groups of microorganisms for assessment of the functioning of the activated sludge plant proved to be a reliable, simple and inexpensive method for monitoring the start‐up and operation of plants.     

Development and application of a resazurin-based biomass activity test for activated sludge plant management

A rapid, robust and cost-effective method of assaying the metabolic activity of the biomass of activated sludge plants would be a valuable process control tool in the wastewater treatment industry. We have developed and optimised a simple colorimetric test protocol, based on the redox dye resazurin, in which levels of reduction of the dye are proportional to cell biomass and respiration rate in both freshly sampled municipal sludges and in a surrogate activated sludge culture, Polytox. The method has been used to assess the impact of trade wastes on the activities of two municipal activated sludge populations of differing characteristics.     

A new technique for monitoring alum sludge conditioning

A technique based on measurements of fluctuations in the intensity of light transmitted through a flowing sludge suspension was used to evaluate polymer performance in alum sludge conditioning. The ratio of the r.m.s. of the fluctuations to the average transmitted light intensity exhibits a well-defined response, usually a substantial increase, to sludge particle aggregation. This aggregation reflects the improvement in sludge filterability as also indicated by concurrent CST measurements. Five polymers, cationic, anionic and nonionic were used in conditioning the sludge. Tests were conducted using a mixer set at 700 rpm with a corresponding velocity gradient of 1900 s⁻¹. The technique was shown to give a very rapid convenient indication of the conditioning effect of polymeric flocculants. It could be very easily adapted to online applications.     

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.     

Effect of extended idle conditions on structure and activity of granular activated sludge

In industry and in tourist areas, periods exist during which no or only very little sewage is produced, and the wastewater treatment facilities have to be set into an idle phase over several days and even weeks. When wastewater is generated again and delivered to the treatment plant, the microorganisms in the activated sludge plant may have lost activity, and the activated sludge flocs may have disintegrated. From previous observation, it is assumed that granular activated sludge is more resistant against long-term storage than activated sludge flocs. Experiments using a laboratory-scale sequencing batch reactor (SBR) were conducted to study the impacts of a 7-weeks anaerobic idle time on structural integrity and metabolic activity of granular activated sludge, and the time required to regain the former operational status of the plant. Oxygen consumption rate (OCR) was used as an indicator to evaluate the metabolic activity of the sludge. The results revealed that the size, color and sedimentation characteristics of the granular sludge did hardly change during the storage period. Sludge activity, however, dropped to values as low as 0.17 mg min(-1)L(-1). After restarting the reactor, the OCR increased within 1 day to a level of 0.57 mg min(-1)L(-1), kept rising at a linear rate in the following days, and reached after 1 week, a value of 5.74 mg min(-1)L(-1) typical for the former activity status. These results imply that granular activated sludge can be stored for a considerably long period of time, and brought into service again relatively quickly. After an idle period of 7 weeks, it took less than a week to regain full capacity of the SBR.     

Biological treatment of low temperature carbonization wastewater by activated sludge process—A case study

This paper outlines the compositional characteristics of wastewater from a low temperature carbonization (LTC), plant manufacturing domestic coke, generating tar and light oil. Wastewater characteristics from this plant show the presence of a variety of pollutants like phenols, ammonia, cyanide, sulphide and thiocyanate in appreciable concentration owing to the absence of byproduct recovery operations. Under suitable conditions, biological treatment of LTC wastewater in a two stage activated sludge process (ASP) mainly results in good removal of BOD (95%) and COD (78%). Concentrations of different phenols and their fate in these treatment units show that the phenols except pyrogallol can be removed efficiently. Ammonia cannot be stabilized to nitrite or nitrate even after maintaining a high sludge retention time (SRT) in the bioreactors. Cyanide removal in these units is very poor. Microbiological status of these units reveals that most of the active biomass is comprised of phenol-utilizing organisms. The system constants for biological unit operations for ASP, like oxygenation capacity of LTC wastewater (a = 0.50 and B = 0.36) and biokinetic constants (Y = 0.13, k_d = 0.12 d⁻¹, μ_max = 0.59 d⁻¹ and k_s = 88.25 mg 1⁻¹), have been evaluated.     

A simple, conceptual mathematical model for the activated sludge process and its variants

A simple structured kinetic model is applied to the activated sludge process. The objective is less to predict exact process performance than to illustrate some of the possibilities and difficulties in producing a comprehensive model for all the process variants. The rate equations are chosen so as to reduce to the Monod equation during balanced growth. Because these rate equations are linear, the cell growth and substrate uptake in a stirred tank can be defined exactly in terms of the average composition of the biomass. It is shown that this is not valid for other forms of rate equations. The stored substrate to protoplasm ratio in the flocs is found to decrease with increasing mean cell residence time. If extracellular biopolymers are included in the stored substrate this corresponds qualitatively to observations of poor flocculation in extended aeration. The model is also applied to the contact stabilization process and is found to be in agreement with the essential process variables.     

A rapid method to measure the solid-water distribution coefficient (Kd) for pharmaceuticals and musk fragrances in sewage sludge

Pharmaceuticals and personal care products are omnipresent in wastewater world-wide. In order to predict their sorption quantities onto sludge in wastewater treatment plants (WWTPs), the solid-water distribution coefficients (Kd values) of selected pharmaceuticals (antiphlogistics, estrogens, lipid regulators, anti-epileptic and cytostatic agents) and polycyclic musk fragrances (HHCB, AHTN) were determined in primary and secondary sludges taken from a German municipal WWTP. For the Kd determination, batches of primary and secondary sludge slurries were spiked with the respective target compounds and slowly stirred under defined conditions (e.g. an argon atmosphere). Finally, the water and solid sludge phases were analysed. The Kd values of pharmaceuticals ranged from <1 to 500 L kg(-1), while those for the polycyclic musk fragrances AHTN and HHCB proved to be up to 5300 and 4900 L kg(-1), respectively. The primary and secondary sludge showed significant differences for some pharmaceuticals such as Diclofenac and Cyclophosphamide due to the different pH and composition of the two sludges. The removal rate from the water phase caused by sorption in a WWTP can be reasonably predicted on the basis of the Kd values.     

ATP,oxygen uptake rate and INT-dehydrogenase activity of actinomycete foams

The purpose of this study was to establish the validity of the INT-dehydrogenase test for determining the biochemical activity of actinomycete foams. Parallel measurements of INT-dehydrogenase activity, adenosine triphosphate and oxygen uptake rate were made on foam samples collected from three different activated sludge plants over a period of several months. Activity levels of actinomycete foams measured in this study were found to be comparable to those of activated sludge as reported in the literature. Good-to-excellent correlations (r² > 0.87) were found between INT-dehydrogenase activity and the alternative parameters. Precision of all assays tested was comparable. The INT-dehydrogenase test can therefore be used in lieu of ATP or oxygen uptake rate assays without sacrifice in either the reliability or reproducibility of results obtained.     

A new reactor concept for sludge reduction using aquatic worms

Biological waste water treatment results in the production of waste sludge. The final treatment option in The Netherlands for this waste sludge is usually incineration. A biological approach to reduce the amount of waste sludge is through predation by aquatic worms. In this paper we test the applicability of a new reactor concept for sludge reduction by the aquatic worm Lumbriculus variegatus. In this reactor concept the worms are immobilized in a carrier material. In sequencing batch experiments, the sludge breakdown in the predation reactor is compared to sludge breakdown in a blank reactor (i.e. without worms). Predation by the worms results in a distinct sludge reduction, which is almost three times higher than in the blank experiment. The worm faeces that are produced after sludge predation have a sludge volume index (SVI) that is approximately half that of the initial waste sludge. Due to the configuration of the predation reactor, waste sludge, worm faeces and worms are separated, which is beneficial to further processing. The obtained results show that the proposed reactor concept has a high potential for use in large-scale sludge processing.     

A model of localised oxygen sinks around bacterial colonies within activated sludge

A new mathematical analysis of diffusional resistances of oxygen in activated sludge is developed. It assumes that the distribution of bacteria within activated sludges flocs are in colonies rather than the usual assumption of a homogeneous distribution of bacteria throughout the sludge. The solutions are for steady-state. The bacterial colony model results in a completely different shape of dissolved oxygen gradient in the floc when compared to the homogeneous bacterial distribution model. The new “bacterial colony” model predicts highly localised oxygen demands around the colony with maximum dissolved oxygen deficits in a 20–40 μm dia floc of 2–3 mg l⁻¹.     

Inhibition coefficient (Ki) determination in activated sludge

A method of measurement of the inhibition coefficient, K_i, of chemicals within the activated sludge has been proposed. It makes possible the objective determination of the influence of non-competitive inhibitors on the reaction rate by means of simple respiration rate measurements with the application of a dissolved oxygen meter. The values of K_i for chromium Cr⁶⁺, for cyanide CN^? and for two pesticides—DDVP and des-methyl DDVP was determined.