Activated Sludge Filamentous Bulking Research Articles

Prediction of activated sludge filamentous bulking using ATP data and neural networks

AbstractNeural networks (NNs) were used to predict the onset of filamentous bulking, as described by trends in stirred sludge volume index, in a pulp and paper activated sludge treatment system. Variables related to activated sludge biomass viability, namely specific oxygen uptake rate (SOUR) and adenosine triphosphate (ATP), were used as inputs to the NN. ATP data were shown to improve NN performance in providing an early warning signal for bulking, both in terms of accuracy and prediction delay. A warning signal system was developed to provide operators with enough time to react and further investigate the causes of bulking.

Clarifying the roles of kinetics and diffusion in activated sludge filamentous bulking

We hypothesized that the growth rates of filaments and floc formers in activated sludge are affected by the combination of kinetic selection (Lou and de los Reyes, Biotechnol Bioeng 92(6): 729-739, 2005b) and substrate diffusion limitation (Martins et al., Water Res 37:2555-2570, 2003). To clarify the influence of these factors in explaining filamentous bulking, a conceptual framework was developed in this study. The framework suggests the existence of three different regions corresponding to bulking, non-bulking, and intermediate regions, based on substrate concentration. In the bulking and non-bulking regions, kinetic growth differences control the competition process, and filaments or floc formers dominate, respectively. In the intermediate region, substrate diffusion limitation, determined by the floc size, plays the major role in causing bulking. To test this framework, sequencing batch reactors (SBRs) were operated with influent COD of 100, 300, 600, and 1,000 mg/L, and the sludge settleability was measured at various floc size distributions that were developed using different mixing strengths. The experimental data in the bulking and intermediate regions supported the proposed framework. A model integrating the two factors was developed to simulate the substrate concentrations at different depths and floc sizes under intermittently feeding conditions. The modeling results confirmed that substrate diffusion limitation occurs inside the flocs at a certain range of activated sludge floc sizes over the operation cycle, and provided additional support for the proposed framework.

Full-Scale Evaluation of a Multi-Component Additive for Efficient Control of Activated Sludge Filamentous Bulking

A multi-component additive formulated for a more efficient control of activated sludge filamentous bulking was evaluated at a full-scale treatment plant experiencing severe filamentous bulking. It was found that, besides offering an immediate improvement of sludge settling, the multi-component additive was able to eliminate the filamentous bacteria causing the bulking. Hence, contrary to ordinary additives, this novel additive yielded immediate as well as long-term improvements in sludge sedimentation upon a few additions. Preliminary lab-scale toxicity tests showed that the treatment of the sludge by the additive should not impart any toxicity to the resulting effluent.

Feasibility of a multi-component additive for efficient control of activated sludge filamentous bulking

Instantaneous improvement of the settling of bulking filamentous activated sludge can be achieved by the addition of a polymer or a large amount (up to 100% of the MLSS concentration) of talc powder to the sludge. Long-term improvement relies on repeated additions, as these additives have no adverse effects on the causative filaments. A multi-component additive was compared to the traditional additives in lab-scale activated sludge units using three highly filamentous sludges from different industrial treatment plants. The study demonstrated that the multi-component additive was superior to the traditional remedies. It was shown that, in the case of severe filamentous bulking, a single addition of the new additive immediately improved sludge settling and exerted a destructive effect on the causative filamentous bacteria. Thus, the latter additive also ensured a long-term sludge sedimentation improvement. The traditional additives exhibited an immediate and short-term effect. The novel additive also retarded sludge rising due to denitrification and it improved sludge dewaterability. The study revealed Nostocoida limicola II, with slightly hydrophobic cell wall, to be somewhat resistant to the quaternary ammonium salt present as biocide in the additive.

Effect of temperature on storage polymers and settleability of activated sludge

This paper describes the effect of tropical temperatures on substrate storage and settleability in an activated sludge sequencing batch reactor (SBR). Substrate uptake, ammonium consumption, oxygen uptake, CO 2 production and poly- β-hydroxyalkanoate formation and consumption were measured at different temperatures (15, 20, 25, 30 and 35°C). Kinetics of the processes were strongly influenced by temperature. All the observable rates except the PHB and NH 4 consumption increased with an increase in temperature. The accumulation of storage polymers strongly depended on temperature. The role of substrate storage for microbial population dynamics and resulting SVI is discussed. The SVI strongly increased with an increased temperature. The results are discussed in the context of the kinetic selection theory of Chudoba et al. [Chudoba, J., Grau, P. and Ottavá, V. (1973) Control of activated sludge filamentous bulking. II. Selection of microorganism by means of a selector. Water Res. 7, 1389-1406.]. From this it becomes evident that the formation of storage polymers should be considered as equally important as the direct competition for substrate based on affinity constants.

Management of toxicity effects in a large wastewater treatment plant

An unusually severe case of toxicity accompanied by activated sludge filamentous bulking was observed at the wastewater treatment plant Sao Paulo-Barueri. Treatment efficiency of the plant, operated without major problems for more than five years before, was significantly hindered for almost six months. Occurrence of toxic shocks was confirmed partly directly but mostly indirectly by inhibition of nitrification and biological phenomena related to toxicity. Several measures adopted, including the recycled activated sludge chlorination, are described in the paper.

Management of toxicity effects in a large wastewater treatment plant

An unusually severe case of toxicity accompanied by activated sludge filamentous bulking was observed at the wastewater treatment plant Sao Paulo-Barueri. Treatment efficiency of the plant, operated without major problems for more than five years before, was significantly hindered for almost six months. Occurrence of toxic shocks was confirmed partly directly but mostly indirectly by inhibition of nitrification and biological phenomena related to toxicity. Several measures adopted, including the recycled activated sludge chlorination, are described in the paper.

The case of both energetic uncoupling and metabolic selection of microorganisms in the OSA activated sludge system

Abstract A modified activated sludge system with anaerobic treatment of returned sludge, named OSA (Oxic‐Settling‐Anaerobic) was studied. The main objective of the research was to create conditions of a physiological stress on microbial growth, resulting in uncoupling of catabolic processes from anabolic ones. This phenomenon, largely described in the literature, is accompanied by energy wastage resulting in biomass yield reduction. The experimental results obtained with a mixed culture (activated sludge) fed on synthetic substrate showed that the anaerobic conditions exerted a kind of selection pressure on microbial metabolism of the activated sludge microorganisms, resulting in metabolic selection of the species being able to favour catabolic pathways. These bacteria, capable of storing polyphosphates under oxic conditions and using them as energy reserves under anaerobic conditions are called poly‐P bacteria. The OSA mixed culture contained about 50 to 60% of these poly‐P bacteria. It has been concluded that the insertion of an anaerobic zone into the returned sludge circuit changed both composition and behaviour of activated sludge microorganisms. The typical phenomena observed in the OSA system were enhanced phosphate removal, reduction of the excess activated sludge production and the suppression of activated sludge filamentous bulking.

Effect of anaerobic conditions on activated sludge filamentous bulking in laboratory systems

The effect of anaerobic conditions on the occurrence of filamentous microorganisms in the biocenosis of activated sludge has been studied in laboratory systems. These systems consisted of an anaerobic completely mixed tank followed by an oxic one. A single oxic completely mixed tank served as a control unit. Synthetic wastewater was used incorporating glucose and ethanol as a carbon source in order to support the growth of filamentous microorganisms in completely mixed tanks. It has been demonstrated that the growth of some filamentous organisms, for instance Type 021N and Sphaerotilus natans, was suppressed under anaerobic conditions as a result of lower rates of polyphosphate depolymerization under anaerobic conditions. However, the positive effect of the anaerobiosis may be eliminated if simultaneous dissimilatory sulphate reduction occurs. In this case filamentous bulking caused by presence of such microorganisms like Thiothrix is possible.

Comment on “Control of activated sludge filamentous bulking—VI. Formulation of basic principles“ by J. Chudoba

Comment on “Control of activated sludge filamentous bulking—VI. Formulation of basic principles“ by J. Chudoba

Control of activated sludge filamentous bulking: Experimental verification of a kinetic selection theory

Two laboratory activated sludge systems, completely-mixed and selector-type, were continuously fed with a multi-component substrate. With excess biomass from both systems, the maximum substrate removal rates, r x.m, and the half-velocity coefficients, K s, were determined by means of a simple respirometric method. The following substrates were tested: glucose, galactose, acetic acid, valeric acid, citric acid, glutamic acid, alanine, tyrosine, methylalcohol, ethylalcohol and phenol. It has been found that both the r x.m and the K s are basically lower with the mixed cultures cultivated in a completely-mixed reactor (filamentous) than with those cultivated in a selector-type reactor (non-filamentous). The results have experimentally verified a kinetic selection theory in mixed cultures published previously.

Control of activated sludge filamentous bulking—VI. Formulation of basic principles

Overgrowing of filamentous micro-organisms in activated sludge is affected by the following factors: (a) composition of treated waste water; (b) actual concentration of dissolved oxygen in an aeration tank; (c) actual concentration of soluble substrate under which micro-organisms grow; (d) technological parameters of the process (sludge loading and age). All these factors were analysed and discussed in the light of the formulated basic principles for control of filamentous bulking.

Control of activated sludge filamentous bulking—III. Effect of sludge loading

Previous experiments have indicated a possibility of controlling the filamentous bulking of activated sludge by cultivating a mixed culture in a system with the plug flow pattern or in a system with a selector. These experiments, however, were conducted at approximately constant sludge load [0·3–0·4 kg BOD 5(kg MLVSS day) −1] and sludge age (4·5–5·0 days) so that the results obtained had only a limited validity. Further experiments were, therefore, carried out in order to find if the previous findings hold also for activated sludge systems with high sludge loads and low sludge ages. The experiments were conducted on four activated sludge systems with different flow patterns: two of them as complete-mixing reactors and the other two as reactors with the plug flow pattern, having dispersion numbers of 0·08 and 0·07. A mixture of starch and peptone was used as the substrate. All systems were operated at sludge ages 2 and 3 days and at sludge loads from 0·5 to 2·3 kg BOD 5(kg MLVSS day) −1. It was found that at sludge loads above 0·5 kg kg −1 day −1 mixed cultures developed in the systems with the plug flow pattern possessed high values of the SVI and contained high portions of filamentous microorganisms. This was found in spite of sufficiently high concentration gradients of the substrate along these systems. It means that plug flow and, consequently, the concentration gradient of the substrate along the activated sludge system may not be the only factor in controlling the selection of microorganisms in a mixed culture. An additional factor must exert an influence on the population dynamics and selection of microorganisms in mixed cultures at high sludge loads and low sludge ages. The experiments have confirmed findings of others that values of the SVI depend on the sludge load. However, different trends of dependence were observed in the systems with different flow patterns. While in the complete-mixing systems the SVI decreased with increasing sludge loading in the systems with the plug flow pattern it increased. A greater phosphorus demand was observed in plug flow systems than in those with complete mixing.

Control of activated sludge filamentous bulking—I. Effect of the hydraulic regime or degree of mixing in an aeration tank

Laboratory experiments were conducted on four activated sludge systems with various flow patterns. The systems were characterized by dispersion numbers which are a numerical expression of the degree of mixing. Perfect mixing has a dispersion number of infinity. The dispersion numbers in the four systems were ∞, 1·06, 0·17 and 0·033. All systems were operated at the same detention period of 8 h and approximately at the same sludge loadings. A mixture of starch and peptone was used as the substrate. The mixed cultures developed in the systems mentioned possessed average SVI values of 517, 300, 91 and 51 ml g−1 respectively. The high SVI values were caused by a high content of the filamentous microorganisms, which consisted mainly of Leucothrix and Sphaerotilus, in the developed mixed cultures. It is concluded that the complete mixing systems tend to lead to excessive growth of the filamentous microorganisms. Aeration systems with a low degree of the axial mixing, i.e. with low dispersion numbers and higher concentration gradients of the substrate along the systems, lead to the growth of non-filamentous and suppress the growth of filamentous microorganisms. It is possible to control the growth of filamentous microorganisms in the mixed cultures by maintaining the concentration gradient of the substrate along the aeration system. The concentration gradient of the substrate depends on the degree of mixing in the aeration system.