The effect of a sewage treatment plant effluent on the faecal coliforms and enterococci populations of the reception river waters

AIMS: A rural sewage treatment plant and the effect of its effluent on the enterococci and faecal coliforms populations of the receiving river waters was evaluated. METHODS AND RESULTS: The enumeration of bacteria was performed by membrane filtration. Diversity and population similarity were analysed using the PhP-plates system. The treatment plant reduces the number of enterococci and faecal coliforms to values similar to those observed upstream. All water samples showed a high diversity for both bacterial populations. A high similarity in the composition and structure, was detected among all the samples. CONCLUSIONS: The impact of the disposal of treated sewage on the river did not modify the composition of either bacterial populations in the river water. SIGNIFICANCE AND IMAPCT OF THE STUDY: The biochemical phenotyping of bacterial populations is a reliable tool for ecological and biodiversity studies. The obtained results provide a better understanding of the sewage treatment process and the impact of the treated sewage effluents in the environment.     

Non-compliance of beaches with the EU directives of bathing water quality: evidence of non-point sources of pollution in Morecambe Bay

Morecambe's three EU designated bathing beaches frequently fail the EU directives, even after a state of the art sewage treatment plant has become operational. We have been using conventional microbiology to look at the seasonality and distribution of indicator and pathogenic bacteria in Morcambe Bay and using molecular methods (polymerase chain reaction (PCR) and pulse field gel electrophoresis (PFGE)) to investigate the pathways by which pathogens reach the bathing waters. We will present data for Morecambe Bay which show that: 1. Failures and passes appear to be associated with the prevailing climatic conditions. 2. Indicator bacteria may not always be derived from sewage effluents. 3. Not all pathogens are distributed in the same way as indicator bacteria. 4. Pathogens such as Campylobacter are as likely to come from birds as from sewage.     

Distribution of the human faecal bacterium Bacteroides fragilis, its bacteriophages and their relationship to current sewage pollution indicators in bathing water

Although several bacteria are currently used as possible indicators of human pathogens in sewage-polluted sea water, they are often viewed as inadequate and especially inadequate as indicators of viral pathogens. This study investigates the distribution of Bacteroides fragilis and closely related Bacteroides spp. and their associated bacteriophages in sea water frequently used for recreational purposes. These organisms may provide a potentially more appropriate indicator. Bacteroides fragilis is one of about 10 species which are loosely placed together in the 'B. fragilis' group. Samples down-current from a sewage outfall were examined for the presence of B. fragilis group organisms and associated bacteriophages. Numbers were correlated with current bacterial and possible viral indicators at these sites. These B. fragilis group isolates were used as hosts to successfully isolate bacteriophages. The host range of these bacteriophages was investigated. It is hoped to expand this study by using these B. fragilis group hosts and their bacteriophages to identify a more suitable, European-wide, indicator of bacterial pathogens which can also be used to detect bacteriophages which are suitable as viral indicators.     

The composition and persistence of faecal coliforms and enterococcal populations in sewage treatment plants

AIMS: The changes in structure and composition of faecal coliforms and enterococcal populations in sewage from different treatment plants, and the elimination of vancomycin- and erythromycin-resistant enterococci (VRE and ERE, respectively) in these treatment plants was analysed to determine any selective reduction. METHODS AND RESULTS: Faecal coliforms, enterococci, VRE, ERE and spores of sulphite-reducing bacteria were enumerated using standard methods. Samples were enriched where necessary in order to isolate antibiotic resistant strains. The structure and composition of these bacterial populations were determined by biochemical fingerprinting and clustering analysis. High diversity and similarity indexes were detected among all the bacterial populations in raw and treated sewage, independently of their origin and the treatment processes employed. Antibiotic resistant strains were detected in all sewage tested and no selective reduction was observed. CONCLUSIONS: The faecal coliforms and enterococci populations did not differ in the sewage samples studied. The vancomycin and erythromycin resistances of the enterococcal populations were similar in the sewage samples. Resistance to both antibiotics persisted after the treatment process independently of raw sewage flow, faecal origin or size of the human population contributing to sewage. However, sewage of mixed origin (human and animal) presented a lower similarity index for the two bacterial populations compared with that of the other human sewage analysed. SIGNIFICANCE AND IMPACT OF THE STUDY: Although a significant reduction in bacterial populations was observed, the persistence of VRE and ERE strains in the same proportions in sewage suggests that there is no selective elimination of bacterial populations during the treatment processes. The ability of antibiotic resistance strains to survive sewage treatment systems should be considered in certain water reuse programmes.     

Distribution and survival of faecal indicator bacteria in the sediments of the Bay of Vidy,Lake Geneva,Switzerland

The purpose of this study was to determine the concentrations and the horizontal distribution of faecal indicator bacteria (FIB) including Escherichia coli and Enterococcus sp. in the bottom sediments of the Bay of Vidy, City of Lausanne, Switzerland. A vertical distribution of FIB in sediments near the municipal wastewater treatment plant (WWTP) outlet was evaluated and their persistence in those sediments was monitored for a period of 90 days. High FIB levels were measured in the sediments sampled near the WWTP outlet pipe and the mouth of the Chamberonne River, at concentrations ranging between 10⁵ and 10⁷ CFU 100 g^?1. FIB levels at 10 cm depth in the sediments near the WWTP outlet pipe ranged between 10⁴ and 10⁵ CFU 100 g^?1, and were still detected in the top 6 cm after 90 days. Results of this study indicate that freshwater sediments of the Bay of Vidy constitute a reservoir of faecal indicator bacteria, which can persist in certain areas of the bay. Possible resuspension of FIB and pathogens may affect water quality and may increase health risks to sensitive populations during recreational activities. FIB survival in sediments for long periods is of considerable significance for the understanding of microbial pollution in water and for the management of risk at specific recreational coastal sites.     

Seasonal migrations of the common Goby,Pomatoschistusmicrops (Kroyer), in Morecambe Bay and elsewhere

Summary Seasonal changes in abundance, and also reproduction, of the gobiid Pomatoschistus microps in intertidal pools on mussel beds at Morecambe, Lancashire, were studied from 1956 to 1961. During winter the shore was largely vacated by this species which returned for breeding purposes in spring. Spawning took place in upper shore pools from April to August. After a planktonic life of between 6–9 weeks, young fishes were recruited to the demersal population usually from June to September. A correlation between seasonal migrations and sea temperature is postulated. Geographical variation in occurrence and extent of migration in P. microps and the related sublittoral P. minutus is considered in relation to minimum winter sea temperatures over the southern Boreal and Baltic sea areas. Offshore winter migration has been found to take place in areas where such temperatures normally fall below 5° C, but not where minimum sea temperature is above 7° C. The effect of the severe winter of 1962–63 on certain populations of P. microps is described.     

De novo formation of organochlorines in a sewage treatment plant

The de novo formation of organochlorines was observed in a municipalsewage treatment plant. Due to this formation, the amount of organically boundhalogens (AOX) increased 15-fold inside the sewage treatment plant. Per day,more than 6 kg of organically-bound chlorine were produced. Thisformation is not based on a metabolism of present organochlorines, it is a denovo formation out of inorganic chloride and organic substrates. The AOXtriggerconcentration in sewage sludge in Germany is 500 mgkg^–1 and was sometimes exceeded by a factor of 10. Noknown anthropogenic organohalogens were found which could explain the elevatedAOX concentrations. Instead many chlorinated compounds could be identifiedwhichwere not known to be of anthropogenic origin. The compound with the highestconcentration was the 3,4-dichlorophenylacetic acid (3,4-CPAc). In one case,more than 1 g kg^–1 of this compound was detected.A slaughterhouse that emits phenylacetic acid is probably the origin of thatformation. In model experiments phenylacetic acid was chlorinated with HOCl butchlorinated phenylacetic acids other than 3,4-CPAc were found. Therefore it canbe excluded that the chlorination in the sewage treatment plant takes place byan abiotic reaction with hypochlorite that might have been introduced there. Weassume that the occurring microorganisms are responsible for the de novoformation in the sewage treatment plant. The obtained knowledge could also beuseful to understand natural chlorination processes.     

The effect of dissolved oxygen,sediment, and sewage treatment plant discharges upon growth,survival and density of Asiatic clams

The biology of Corbicula fluminea, the Asiatic clam, in the Vermilion River, Louisiana, as affected by sediment, dissolved oxygen (DO) levels, and sewage treatment plant (STP) effluents was investigated. A point source of high DO water to the Vermilion River established a gradient of DO that decreased as the river moved towards the Gulf of Mexico. Lowering DO levels were exacerbated by municipal sewage treatment plant discharges in the 20 km reach studied. Low dissolved oxygen was associated with reduced Corbicula density in the river and 30-day in-stream growth studies (weight and length) demonstrated that low DO inhibited growth. Generally, if DO was < 1.0 mg l^–1 in sediment pore water and/or < 3.0 mg l^–1 at the sediment-water interface, growth was significantly impaired (p < 0.05). Corbicula experienced substantial mortality near the STP discharges (up to 70% in 30 days) and laboratory toxicity tests with Ceriodaphnia dubia, a sensitive cladoceran, also strongly suggested discharges were chronically toxic at 6.25–25.0% effluent. Respiration experiments along with environmental measurements of DO, temperature, and STP discharge chemistry support a hypothesis that clam populations are adversely affected by the suite of environmental conditions present in the Vermilion River. Further, growth studies were consistent with observed population densities in situ.     

Effects of a sewage treatment plant outlet pipe extension on the distribution of contaminants in the sediments of the Bay of Vidy, Lake Geneva, Switzerland

In 2001, the municipality of Lausanne extended the outlet pipe of the sewage treatment plant into the Bay of Vidy (Lake Geneva, Switzerland) as a measure to reduce bacterial water pollution and sediment contamination close to the lake beaches. The aim of the present study was to assess the impact of this measure. Lake bottom sediments were collected and analyzed for grain size, organic matter, organic carbon, nitrogen, phosphorus, heavy metals and hydrophobic organic compounds to evaluate their concentration and spatial distribution. Our results demonstrate that, compared to results obtained before the outlet pipe prolongation, the surface area of highly contaminated sediments was reduced by one third after the pipe extension. However, contaminant concentrations are still high and the accumulation of pollutants may represent a significant source of toxicity for benthic organisms. One concludes that contaminant reduction at the source will be necessary for a further improvement.     

Phototrophic purple and green bacteria in a sewage treatment plant.

In all purification stages of a biological sewage treatment plant, phototrophic bacteria were detected by the method of viable cell counts. The predominant species identified belonged to the genus Rhodopseudomonas of purple nonsulfur bacteria. The number of phototrophic bacteria was highest in wastewater containing sludge. In activated sludge, an average of 10(5) viable cells/ml was found; the number depended upon concentration of sludge rather than on seasonal changes in light conditions in the course of a year. Bacteriochlorophyll a was extracted from activated sludge. Relative to the viable counts of phototrophic bacteria, the content of bacteriochlorophyll a was 5- to 10-fold higher than that of three representative pure cultures. By incubation of activated and digester sludge under different environmental conditions, it was shown that phototrophic bacteria can complete with other bacteria only under anaerobic conditions in the light.     

Detection and enumeration of Listeria monocytogenes in a sewage treatment plant in Iraq

Listeria monocytogenes was isolated from a sewage treatment plant in Baghdad, Iraq, at all stages of treatment. The treatment processes did not yield a sewage sludge cake or a final discharge free of listerias. The agricultural practice of using such sewage products as fertilizers could become a route of spreading the organism in Iraq, particularly by infecting animals that consume vegetation in fields spread with such sewage. Dewatering of sewage reduced the number of L. monocytogenes but long periods of exposure to sun would be needed to obtain a 'safe' sewage sludge cake.     

Detection and enumeration of Listeria monocytogenes in a sewage treatment plant in Iraq

Listeria monocytogenes was isolated from a sewage treatment plant in Baghdad, Iraq, at all stages of treatment. The treatment processes did not yield a sewage sludge cake or a final discharge free of listerias. The agricultural practice of using such sewage products as fertilizers could become a route of spreading the organism in Iraq, particularly by infecting animals that consume vegetation in fields spread with such sewage. Dewatering of sewage reduced the number of L. monocytogenes but long periods of exposure to sun would be needed to obtain a 'safe' sewage sludge cake.     

Detection of low numbers of Salmonella in environmental water, sewage and food samples by a nested polymerase chain reaction assay

A polymerase chain reaction (PCR) assay with two nested pairs of primers selected from conserved sequences within a 2.3 kb randomly cloned DNA fragment from the Salmonella typhimurium chromosome was developed. The nested PCR assay correctly identified 128 of a total of 129 Salmonella strains belonging to subspecies I, II, IIIb and IV. One strain of Salm. arizona (ssp. IIIa) tested negative. No PCR products were obtained from any of the 31 non-Salmonella strains examined. The sensitivity of the assay was 2 cfu, as determined by analysis of proteinase K-treated boiled lysates of Salm. typhimurium. The performance of the assay was evaluated for environmental water, sewage and food samples spiked with Salm. typhimurium. Water and sewage samples were filtered and filters were enriched overnight in a non-selective medium. Prior to PCR, the broth cultures were subjected to a rapid and simple preparation procedure consisting of centrifugation, proteinase K treatment and boiling. This assay enabled detection of 10 cfu 100 ml(-1) water with background levels of up to 8700 heterotrophic organisms ml(-1) and 10000 cfu of coliform organisms 100 ml(-1) water. Spiked food samples were analysed with and without overnight enrichment in a non-selective medium using the same assay as above. Nested PCR performed on enriched broths enabled detection of <10 cfu g(-1) food. Variable results were obtained for food samples examined without prior enrichment and most results were negative. This rapid and simple assay provides a sensitive and specific means of screening drinking water or environmental water samples, as well as food samples, for the presence of Salmonella spp.     

Persistence, transmission, and virulence characteristics of Aeromonas strains in a duckweed aquaculture-based hospital sewage water recycling plant in Bangladesh

The persistence and transmission of Aeromonas in a duckweed aquaculture-based hospital sewage water treatment plant in Bangladesh was studied. A total of 670 samples from different sites of the hospital sewage water treatment plant, from feces of hospitalized children suffering from diarrhea, from environmental control ponds, and from feces of healthy humans were collected over a period of three years. In total, 1,315 presumptive Aeromonas isolates were biochemically typed by the PhenePlate rapid screening system (PhP-AE). A selection of 90 representative isolates was further analyzed with PhenePlate (PhP) extended typing (PhP-48), fatty acid methyl ester analysis, and amplified fragment length polymorphism (AFLP) fingerprinting. In addition, the prevalence of the putative virulence factors hemolysin and cytotoxin and the presence of the cytolytic enterotoxin gene (AHCYTOEN) were analyzed. Aeromonas was found at all sites of the treatment plant, in 40% of the samples from environmental control ponds, in 8.5% of the samples from hospitalized children suffering from diarrhea, and in 3.5% of samples from healthy humans. A significantly high number of Aeromonas bacteria was found in duckweed, which indicates that duckweed may serve as a reservoir for these bacteria. PhP-AE typing allowed identification of more than 192 distinct PhP types, of which 18 major PhP types (MTs) were found in multiple sites and during several occasions. AFLP fingerprinting revealed the prevalence of genotypically indistinguishable Aeromonas isolates among certain PhP MTs recovered from different sampling occasions and/or at multiple sites. Hemolytic and cytotoxic activities were observed in 43% of the tested strains, whereas 29% possessed the cytolytic enterotoxin gene AHCYTOEN. Collectively, two specific MTs associated with diarrhea were shown to exhibit high cytotoxicity. Furthermore, all tested isolates of these major types were positive for the cytolytic enterotoxin gene. In conclusion, our data indicate that certain phenotypically and genotypically stable clonal lineages of Aeromonas have persisted in the treatment system for a prolonged period and might spread from the hospitalized children suffering from diarrhea to fish produced for human consumption through the sewage water treatment system.     

Antibiotic resistance of native and faecal bacteria isolated from rivers, reservoirs and sewage treatment facilities in Victoria, south-eastern Australia

The incidence of resistance to ampicillin, chloramphenicol, kanamycin, nalidixic acid, neomycin and streptomycin was significantly greater (P < 0.001) in native heterotrophic bacteria than in Escherichia coli isolated from a range of sites along the Yarra River in south-eastern Australia. There was no significant difference in the incidence of resistance between native and faecal bacteria to tetracycline. Both groups were almost totally resistant to penicillin. Multivariate analyses indicated little clear spatial pattern in the incidence of resistance in native bacteria from upstream vs downstream sites along the Yarra River. In contrast, E. coli isolated from upstream (rural) sites tended to have a lower incidence of resistance than isolates from downstream (urban) sites. These findings have implications for the use of antibiotic resistance as a bacteriological water quality parameter.     

Occurrence and seasonal variation of airborne gram negative bacteria in a sewage treatment plant

A study was carried out to determine the microbial density and the seasonal variation of airborne Gram negative bacteria in a sewage treatment plant. Sampling was made at 16 sites and the settle plate technique was used. Of the 201 samples examined, 43.2% revealed fecal coliforms (mean value = 14 cfu/p/h), 53% Pseudomonas spp. (mean value = 11 cfu/p/h), 46.5% Shigella spp. (mean value = 13 cfu/p/h), 3% Legionella spp. (mean value = 2 cfu/p/h) and 2% Salmonella (mean value = < 1 cfu/p/h). 72% of the samples contained "other" Gram negative bacteria such as Aeromonas hydrophila, Serratia marcescens, Enterobacter cloacae and others. With the exception of Legionella spp. and Salmonella, all other bacteria were more frequent and numerous in the October-March period, when temperatures were lower and humidity higher. Although the oxidation tanks were covered overall contamination was nevertheless high, thus presenting a potential health risk for plant workers.     

Distribution and seasonality of microbial indicators and thermophilic campylobacters in two freshwater bathing sites on the River Lune in northwest England

Two freshwater bathing sites, the Crook O'Lune and the University Boathouse, on the River Lune in the north-west of England, were monitored over a 2 year period for the faecal indicators, faecal coliforms and faecal streptococci, the pathogens, Salmonella and Campylobacter, and compliance with the EU Directive on Bathing Water Quality. Faecal indicator numbers showed no seasonal variation, with numbers in the bathing season similar to those in the non-bathing season. They were consistently above the EU Guideline and Imperative standards so that if the EU Bathing Water Quality Directive (76/160/EEC) were applied, neither site would comply. Faecal indicator numbers in the sediments were an order of magnitude higher than in the overlying water. Campylobacter numbers showed seasonal variation in the water with higher counts in winter than in the summer, although numbers were low. Higher numbers were found in the sediments but there was no seasonal variation. Analysis of various inputs showed that indicators and campylobacters came from a mixture of sources, namely a sewage treatment works, agricultural run-off, streams and mallards. Microbial numbers in the water at the Crook O'Lune, which is closer to the sources of pollution, were twice those at the Boathouse. In the sediments they were six to eight times higher. Faecal coliforms were all identified as Escherichia coli of which 80% were a single biotype. Faecal streptococci were all enterococci of which 55% were E. avium, 38% E. faecalis and 7% E. durans. Salmonella was not isolated from either the water column or the sediments. Campylobacters were mainly Camp. jejuni, followed by Camp. coli, UPTC and Camp. lari.