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Extracellular polymeric substances (EPS) were quantified in flocculent and aerobic granular sludge developed in two sequencing batch reactors with the same shear force but different settling times. Several EPS extraction methods were compared to investigate how different methods affect EPS chemical characterization, and fluorescent stains were used to visualize EPS in intact samples and 20-m cryosections. Reactor 1 (operated with a 10-min settle) enriched predominantly flocculent sludge with a sludge volume index (SVI) of 120 ؎ 12 ml g ؊1 , and reactor 2 (2-min settle time) formed compact aerobic granules with an SVI of 50 ؎ 2 ml g ؊1 . EPS extraction by using a cation-exchange resin showed that proteins were more dominant than polysaccharides in all samples, and the protein content was 50% more in granular EPS than flocculent EPS. NaOH and heat extraction produced a higher protein and polysaccharide content from cell lysis. In situ EPS staining of granules showed that cells and polysaccharides were localized to the outer edge of granules, whereas the center was comprised mostly of proteins. These observations confirm the chemical extraction data and indicate that granule formation and stability are dependent on a noncellular, protein core. The comparison of EPS methods explains how significant cell lysis and contamination by dead biomass leads to different and opposing conclusions.The efficiency of biological wastewater treatment depends, first, upon the selection and growth of metabolically capable microorganisms and, second, upon the efficient separation of those organisms from the treated effluent. Bacteria usually aggregate to form suspended flocs, which can cause bulking and foaming problems if filamentous bacteria are present. Activated sludge flocs also settle relatively slowly, requiring large primary and secondary settling tanks before clear effluent can be released. Alternatively, aerobic granular sludge aggregates have been formed in sequencing batch reactors (SBRs) with short fill periods and various substrates (1a, 13, 15). As opposed to flocs, granules are dense and have high settling velocities. They can be described as a collection of self-immobilized cells into a somewhat spherical form and are considered to be a special case of biofilm growth (10).Microbial aggregates form biofilms by creating a network of cells and extracellular polymeric substances (EPS), which include any substances of biological origin (9). The abbreviation "EPS" has often been expanded to extracellular polysaccharides or exopolysaccharides. However, EPS have been shown to be a rich matrix of polymers, including polysaccharides, proteins, glycoproteins, nucleic acids, phospholipids, and humic acids. EPS are typically reported to aid in the formation of a gel-like network that keeps bacteria together in biofilms, cause the adherence of biofilms to surfaces, and protect bacteria against noxious environmental conditions (24).Because EPS are a major component of cell flocs and biofilms, they are hypothesized to play a central ...

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The traditional wastewater management concept (urban wastewater collection system plus treatment of the wastewater in a central treatment plant) has been successfully applied over many decades in densely populated areas of industrialized countries. Whether this technology is of ultimate wisdom must be questioned, especially considering the urgent need for improved sanitary infrastructures in developing countries. The problem is that the costs for implementing a centralized system in mega-cities, in particular the investment costs for the sewer system, are exorbitant. Decentralized wastewater management systems, with the wastewater treated close to where it is generated, are being considered by various researchers and institutions including the World Bank as an alternative to the traditional centralized system. The degree of technological sophistication that should be applied is under dispute, however. In this paper, we advocate development and application of high-tech on-site treatment plants, designed and fabricated by modern industrial methods. When mass produced, the costs for manufacturing such package plants can presumably be kept at a relatively low level. The plants should be delivered in a “user ready” state. Local plumbers may connect toilet bowls and sinks and washing machines, but may not be involved in the manufacturing of the treatment system. The plant should produce an effluent which is hygienically safe and can subsequently be utilized for toilet flushing, washing clothes, cleaning floors or watering lawns. In order to keep the plants operating properly, they should controlled by remote sensing, and maintained by specialized service enterprises. The conceptual design of such a compact plant is discussed in the form of a case study.

A sequencing batch reactor (SBR) was used to investigate the generation of different granules cultured under aerobic and alternating anaerobic/aerobic conditions. The reactor was fed with synthetic wastewater. A substrate loading rate of 3.6 kg COD/(m3 day) was applied. Granules of heterotrophic microorganisms were formed. After the first experimental period of 8 weeks the average granule diameter was 3.2 mm. In the second period, alternating anaerobic/aerobic conditions were applied to form granular sludge with an average diameter of 3.0 mm. An isopycnic centrifugation procedure was used to determine the characteristic density of the aerobic granular sludge. The average density of the granular sludge was 1.044 g/ml and 1.048 g/ml, respectively. In free-settling tests the final settling velocity of single aggregates was examined to estimate porosity. Settling velocities up to 2.0 cm/s could be measured. Calculations based on the experimental results showed an average granula porosity of 72% for the first run and 65% average porosity for the second run. This paper indicates the validity of general assumptions in free-settling tests.