Semi-continuous Activated Sludge Research Articles

Application of a molecular based approach for the early detection of short term 3-chloroaniline shock loads on activated sludge bacterial community and functionality

Microbial processes are central elements in wastewater treatment plants (WWTPs) to mineralize the organic matter, to degrade pollutants and to decrease the amount of suspended solids. This activity can be disrupted by organic and inorganic pollutants present in wastewater streams. Hence, it is of primary importance to investigate and monitor the structure and functionality of the sludge-resident microbial communities. We simulated a 3-chloroaniline (3-CA) shock load in 3-CA adapted and non-adapted semi-continuous activated-sludge (SCAS) reactors to selectively stress the Ammonia Oxidizing Bacteria (AOB). Recently developed setting-independent theoretical interpretation of molecular DNA and RNA fingerprinting patterns were used to evaluate the responses of the microbial populations. Ammonium accumulation in treated reactors upon 3-CA addition confirmed the disruption of the functionality under stress conditions. Molecular analyses coupled to their interpretation highlighted that shock loaded reactors clustered separately from non-treated ones, especially when AOBs community was specifically targeted. Furthermore, the interpretation of RNA-based analyses, as compared to DNA-based ones, allowed to more promptly depicting shifts in a stressed community. We showed that the use of RNA-based molecular tools in combination with a new set of parameters is a powerful tool to link functional failures with microbial structure modifications in WWTPs, providing a potential tool for a rational optimization of the processes (Microbial Resource Management - MRM).

Bioaugmentation of activated sludge by an indigenous 3-chloroaniline-degrading Comamonas testosteroni strain, I2gfp.

A strain identified as Comamonas testosteroni I2 was isolated from activated sludge and found to be able to mineralize 3-chloroaniline (3-CA). During the mineralization, a yellow intermediate accumulated temporarily, due to the distal meta-cleavage of chlorocatechol. This strain was tested for its ability to clean wastewater containing 3-CA upon inoculation into activated sludge. To monitor its survival, the strain was chromosomally marked with the gfp gene and designated I2gfp. After inoculation into a lab-scale semicontinuous activated-sludge (SCAS) system, the inoculated strain maintained itself in the sludge for at least 45 days and was present in the sludge flocs. After an initial adaptation period of 6 days, complete degradation of 3-CA was obtained during 2 weeks, while no degradation at all occurred in the noninoculated control reactor. Upon further operation of the SCAS system, only 50% 3-CA removal was observed. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes revealed a dynamic change in the microbial community structure of the activated sludge. The DGGE patterns of the noninoculated and the inoculated reactors evolved after 7 days to different clusters, which suggests an effect of strain inoculation on the microbial community structure. The results indicate that bioaugmentation, even with a strain originating from that ecosystem and able to effectively grow on a selective substrate, is not permanent and will probably require regular resupplementation.

GAC-Amended UASB Reactor for the Stable Treatment of Toxic Textile Wastewater

A feasibility study was carried out in the laboratory for the sequential anaerobic/aerobic treatment of textile wastewater. The process units consisted of an anaerobic UASB (upflow anaerobic sludge blanket) reactor and a SCAS (semi-continuous activated sludge) reactor. A contact-sorption layer with GAC (granular activated carbon) was provided at the bottom of the conventional UASB reactor. The raw textile wastewater first passed through the GAC bed and then through the sludge bed. By means of the GAC bed, the top-layer granular sludge was protected from toxicants. Biological regeneration of GAC, which was enhanced via a recycle flow, was demonstrated. The combined GAC-UASB and SCAS treatments allowed a stable performance and a COD (chemical oxygen demand) and colour removal of 98 and 95 %, respectively.

Nonylphenol degradation in lab scale activated sludge units is temperature dependent

Nonylphenol (NP) is considered to be a pseudo-estrogen and moreover is the most recalcitrant intermediate of the nonylphenol polyethoxylates. The latter are an important group of nonionic surfactants with worldwide applications. The behaviour and fate of nonylphenol during activated sludge treatment was studied using laboratory scale reactor units. It appeared that the NP added at concentrations of 8.33mg/l was almost totally removed and biodegraded when the reactors were operated at 28°C. By lowering the temperature from 28 to 10–15°C, elimination capacities decreased to 13–86%, depending on the process conditions. Upon re-establishing the temperature at 28°C, the accumulation of NP in the sludge could be counteracted. It was also demonstrated that the capacity of semi-continuous activated sludge (SCAS) to degrade NP was extended when the feed was made up with effluent from a full-scale activated sludge. Yet, the latter appeared also capable of rendering small amounts (20–100μgNP/g TSS) less bio-removable.

Does the semi-continuous activated sludge (SCAS) test predict removal in secondary treatment?

The semi-continuous activated sludge (SCAS) test was formalized by the U.S. Soap and Detergent Association in 1965. The SCAS procedure has also been adopted by the Organization for Economic Cooperation and Development (OECD) as a test for inherent biodegradability and by the U.S. EPA as a test guideline (40CFR 835.3120) under the Toxic Substances Control Act. To investigate whether the SCAS test may be used to predict removal in full-scale activated sludge treatment systems, we first collected all available SCAS data for organic chemicals, and then retrieved data from full-, pilot- or bench-scale continuous-feed activated sludge (CAS) studies for the chemicals that had SCAS data. The intersected file was subjected to statistical analysis. Conclusions were as follows: (i) SCAS data were strongly clustered at high (> 90 %) removal; (ii) for SCAS removal > 90 %, it is probable that removal in the field will be > 50 %; (iii) however, for SCAS removal < 90 % adequate treatability cannot be predicted with confidence.

Biological removal of EDTA in conventional activated-sludge plants operated under alkaline conditions

Semicontinuous activated-sludge (SCAS) units inoculated with activated sludge from a plant treating predominantly domestic wastewater were used to study EDTA removal from wastewater at different pH values. Almost complete removal of EDTA was found in units maintained at pH > 8·0, but high EDTA removal was obtained only in SCAS units run with sludge retention times ≥ 12 days. A maximum EDTA removal rate of 0·2 kg EDTA/m 3/day was achieved in the SCAS units. A full-scale activated-sludge system operating under alkaline conditions provided high removal percentages, confirming the removal of EDTA in activated-sludge systems as established in the SCAS tests. The results in both laboratory and full-scale activated-sludge units showed that a reduction of more than 90% of the incoming EDTA was attainable. Ratios of biological oxygen demand to theoretical oxygen demand of > 0·6 in closed-bottle tests, inoculated with either sludge from a full-scale treatment plant or an SCAS unit, proved that EDTA was removed by biodegradation. These results clearly demonstrated that EDTA-containing wastewater is amenable to activated-sludge treatment in conventional plants operated under alkaline conditions.

Improvement of activated sludge performance by the addition of Nutriflok 50 S

By means of rigorously controlled lab-scale activated sludge systems operated in parallel, the effect of the addition of a nutritive supplement on the overall performance of these systems was verified. Nutriflok 50 S is a commercially available product, containing nutrients and flocculating agents. In a first series of tests by means of SCAS (semi-continuous activated sludge) reactors, fed with synthetic wastewater, the positive effect of the supplement (dosed at 5% of the chemical oxygen demand (COD) load) on the sludge volume index (SVI) (39% improvement) and the residual COD (40% improvement) was demonstrated. In a second series, an industrial wastewater was used in a benchscale set-up according to the OECD procedure. The overall efficiency and sludge sedimentation characteristics were compared for two parallel activated sludge systems continuously fed with pharmaceutical wastewater. In the control no additive was given; the other reactor received on a daily basis a dose of Nutriflok 50 S corresponding to 10% of the COD load. The performance of the Nutriflok 50 S supplemented reactor was found to be statistically better in terms of sedimentation characteristics, nitrification and COD removal than the control. Especially when operated under winter conditions (10°C) and at higher sludge loading rates (Bx = 0.26 kg COD/kg VSS.d) the COD removal efficiency was about 35% higher in the treated reactor. Moreover, nitrification could be maintained in the supplemented reactor at low temperatures, whilst it became minimal under those conditions in the control reactor. Also in the second series of tests, sludge sedimentation characteristics improved with Nutriflok 50 S. The SVI was 40% lower for the Nutriflok 50 S amended sludge and the recycled sludge was 27% more concentrated. When operated at higher temperatures (20–26°C) the amended sludge was less sensitive to denitrification linked flotation in the settler. Microscopic examination of the sludge revealed a more diverse microbial community and the presence of higher trophic organisms in the supplemented reactor. These results indicate a potential for considerable improvement, not only of the overall conversion efficiency, but also of the sludge management characteristics when Nutriflok 50 S is dosed to the activated sludge.

Mater-Bi: Properties and biodegradability

This paper examines the biodegradability of a new class of materials based on starch and vinylalcohol copolymers, which have been commercialized under the Mater-Bi trademark. Particular attention is given to the biodegradation process for natural and synthetic components of different Mater-Bi grades for film blowing in an aerobic respirometric test, in a SCAS (semicontinuous activated sludge) test, and by submersion in lake water. The correlation between morphology and biodegradation behavior is also considered. Taking into account the prior art on biodegradation of insoluble substrates, a two-step mechanism is proposed for Mater-Bi products.

Fate in sewage of a recombinant Escherichia coli K-12 strain used in the commercial production of bovine somatotropin.

The fate of a derivative of Escherichia coli strain W3110G [pBGH1], a strain used for production of bovine somatotropin, was examined in semi-continuous activated sludge (SCAS) units. A nalidixic acid-resistant derivative of W3110G [pBGH1], strain LBB270 [pBGH1], was used to facilitate tracking. SCAS units (300 ml) containing municipal mixed liquor were operated on a daily cycle of 23 h aeration and 1 h setting followed by decanting of clear supernatant (175 ml) and refilling with fresh primary effluent. SCAS units were inoculated with two concentrations of E. coli LBB270 [pBGH1] and operated for 200 h. Viable levels of E. coli LBB270 [pBGH1] were measured daily in aerated mixed liquor and decanted supernatant. Viable counts in the mixed liquor decreased from 10,000- to 100,000-fold in less than 200 h. Losses of E. coli LBB270 [pBGH1] in decanted supernatants accounted for less than 2-fold of the total losses observed in the SCAS units. The E. coli LBB270 [pBGH1] was not evenly distributed in the mixed liquor, but became preferentially associated with the settleable floc. These results show that E. coli LBB270 [pBGH1] was unable to survive in municipal sludge even when inoculated at concentrations greater than, or comparable to, levels of indigenous microorganisms.

High performance liquid chromatographie analysis of intact and partially biodegraded linear alkylbenzene sulfonates

AbstractA high performance liquid chromatography (HPLC) method for the determination of intact and partially degraded linear alkyl‐benzene sulfonate (LAS) was developed. The LAS degradation products resulting from a semicontinuous activated sludge (SCAS), a die‐away CO2 and a simulated river die‐away study were quanti‐tatively determined by HPLC equipped with a reversed‐phase column using a tetrahydrofuran/water/Pic A solution as the mobile phase. The column effluent was monitored with a fluorescence spectrophotometer that was operated at an excitation wavelength of 232 nm and an emission wavelength of 290. Compounds investi‐gated included both single‐and mixed‐carbon‐range materials. The HPLC method shows good correlations with MBAS for intact LAS material. The most significant advantage of this method over MBAS is it ability to quantitatively determine partially degraded intermediates and the disappearance of those intermediates. This method, when using the fluorescence detection system, is selective for sulfonated ring structures with more than one alkyl carbon. The sensitivity of the method is in the 0.05‐ppm range. It can be used not only for samples from laboratory experiments but also for sewage plant influents, effluents and river waters.