Laboratory Sequencing Batch Reactor Research Articles

Final Clarification by Integrated Filtration within the Activated Sludge Aeration Tank

A laboratory sequencing batch reactor (SBR), integrating a novel filtration system, was used to treat wastewater from a cheese factory. For an average influent CODtot of 1,000 mg l−1 and at an HRT of 8 d, the SBR-Filtration system yielded an overall efficiency of 94.5% in terms of COD removal, and an effluent suspended solids (SS) concentration close to 0 mg l−1. Throughput fluxes as high as 443 l m-2 h−1 could be reached. No permanent clogging or decrease in permeability of the filtration step was observed over the 12 d testing period. The effect of solids concentration on filtration was assessed by increasing, stepwise, the MLSS concentration in successive stages. The food to microorganism ratio (F/M) was maintained almost constant by increasing the influent load proportionately to the increase in biomass. This was done by adding powdered milk waste to the real wastewater. As a result of rapid increases in influent COD, changes in composition and loading rates, and a lack of nutrients during this phase of experiments, steady state conditions were interrupted. Consequently, the biomass would not flocculate well and the SVI increased. The decrease in filtration efficiency was thought to be due to the transient biological state of the biomass, rather than to the concentration increase itself. An attempt to corroborate this observation was made by systematically decreasing the mixed liquor concentration in the reactor by dilution with water. Flux rates remained constant, regardless of the variation of MLSS concentration.

Bacteria and Protozoa Population Dynamics in Biological Phosphate Removal Systems

Population dynamics of polyphosphate-accumulating bacteria (PP bacteria) was studied in a laboratory sequencing batch reactor simulating anaerobic-oxic sludge system. The competition between PP bacteria and another microorganism (“G bacteria”) for anaerobic-oxic utilization of acetate as the sole source of organic carbon was observed. The competition was found to be seriously influenced by protozoan and metazoan grazing: Predation-resistant “G bacteria” forming large compact flocs outcompeted PP bacteria. Several breakdowns of enhanced biological phosphorus removal were observed. The first one was related to the development of an euglenid flagellate Entosiphon sulcatus and attached ciliates Vorticella microstoma and V. campanula. The second system collapse was connected with a rapid proliferation of rotifers. An alternative-prey predation was thought to be a mechanism of PP bacteria elimination.

Efficiency of sequencing batch reactor (SBR) in the removal of selected microorganisms from domestic sewage

The relationships between the loading factor ( L i) and BOD 5, COD, TSS, total coliform, fecal coliform and coliphage removals were explored using three laboratory SBRs receiving a medium-to-low strength domestic sewage. The SBRs were operated with different FILL/REACT ratios in a 6-h cycle. Not unexpectedly results showed that increases in L i led to decreases in the removals of BOD 5, COD, TSS and potential pathogen indicators. However, low SVIs (Sludge Volume Index) in the SBR need not necessarily mean good solids settleability. Good settleability is, however, necessary for good TSS removal as it led to better removals of total BOD 5, total COD and indicators of potential pathogens. During FILL, fermentation reactions probably occurred and this resulted in up to 86% reduction of the initial dissolved BOD 5 concentration. Degradation of waste then continued into the REACT period. This preliminary assessment showed that the SBR is, potentially, a viable option for domestic wastewater treatment, especially since the aeration time required for treatment to achieve comparable effluent quality is shorter than the conventional continuous activated sludge systems which are usually operated with about 3–8 h of aeration time.

Competition between PolyP and non‐PolyP bacteria in an enhanced phosphate removal system

ABSTRACT: The competition between polyphosphate accumulating bacteria (PolyP bacteria) and a group of microorganisms not accumulating polyphosphate (tentatively named “G bacteria”) was observed in a laboratory sequencing batch reactor exhibiting enhanced biological phosphate removal (EBPR). The “G bacteria” were able to dominate the anaerobic‐oxic system even though acetate was readily available. When acetate was used as the sole source of organic carbon, however, PolyP bacteria were able to compete successfully with “G bacteria.” The molar ratio of phosphate released to acetate taken up in the anaerobic stage varied from 0 to 0.78 and depended on the ratio of the numbers of PolyP bacteria to “G bacteria” in the activated sludge.

Competition between polyphosphate and polysaccharide accumulating bacteria in enhanced biological phosphate removal systems

The competition between polyphosphate accumulating bacteria (PP bacteria) and another group of microorganisms (tentatively named “G bacteria”) has been observed in laboratory sequencing batch reactors exhibiting enhanced biological phosphate removal (EBPR). The “G bacteria”, which accumulate polysaccharide instead of polyphosphate, were able to dominate the anaerobic-oxic system even though acetic acid was readily available. When acetate was used as the sole source of organic carbon in an anaerobic-oxic sequencing batch reactor, however, PP bacteria successfully competed for acetate with “G bacteria”. The molar ratio of phosphate released to acetate taken up in the anaerobic stage varied from 0 to 0.78 and depended on the ratio of the numbers of PP bacteria to “G bacteria” in the activated sludge.