No abstract

A series of experiments to determine the survival characteristics of environmental and faecal coliforms in a 1·3 km long experimental pipe distribution system is described. In the first experiments, tertiary treated effluent (103–104 coliforms ml−1) was inoculated directly into the distribution system. Coliform organisms were not detected in any samples taken downstream of the inoculation point. By comparison, laboratory jar tests showed low level survival for coliforms at the same chloramine residuals (0·3 mg l−1) for up to 48 h. In the second series of experiments, a by‐pass pipe in the experimental distribution system was isolated, drained, and filled with tertiary treated effluent (103–104 coliforms ml−1) to simulate the conditions in a dead‐end. Coliform numbers were monitored and found to decrease rapidly, but they were still detectable at low levels after 7 weeks. The water in the by‐pass section was then released into the main pipe‐rig and sampled downstream. No coliforms were detected in water samples or in samples swabbed from the pipe walls. Finally, the flow in the main pipe‐rig and in the by‐pass was increased to dislodge any deposits and biofilm into the water. The absence of coliforms in any water samples taken during or after the flow increases is contrary to the widely accepted understanding that coliforms survive and grow in biofilms on pipe walls.

Aims: This study examined the suitability of three analytical methods for isolating and enumerating Escherichia coli from conventionally treated sewage sludge. Methods and Results: Crude sewage, mesophilic anaerobic digested (MAD) sludge, and final product sludge samples were taken from six sewage treatment works for analysis. Two of the three methods tested were membrane filtration techniques, utilizing chromogenic E. coli/coliform (CEC) media and membrane-lactose glucuronide agar (MLGA); the third method was a most probable number (MPN) technique utilizing Colilert in Quantitray 2000 (Idexx). The methods were evaluated for variation, consistency, false-positive and false-negative results, as well as method correlation. The methods gave good and consistent recovery of E. coli for a range of conventionally treated sewage matrices. All of the methods had a false-positive rate of <3%, although MLGA had a high false-negative rate (35AE5%) compared with Colilert (3AE81%) and the CEC method (6AE75%). This resulted in slightly lower presumptive counts but comparable numbers of confirmed counts. Conclusions: The three detection methods tested, chromogenic, MLGA and Colilert gave comparable recoveries, and did not vary by greater than one order of magnitude (1 log). Significance and Impact of the Study: Forthcoming revisions to the Use of Sludge in Agriculture Regulations (1989) will categorize sewage sludge as untreated, conventionally treated or enhanced treated in accordance to microbiological standards. The standard will be based upon numbers of E. coli removed through the sludge treatment process and the numbers remaining in the final product. It is recommended that the Colilert 2000 (Idexx, Westbrook, Maine) and CEC methods would be equally suitable to assess the reduction of indigenous E. coli in conventionally treated sludges, and that MLGA be used with follow-up confirmatory testing.

Test blocks of beech (Fagus sylvatica) and Scots pine (Pinus sylvestris) were buried in fresh, brackish, and seawater anaerobic muds for periods ranging between 1 and 18 months. At appropriate time intervals the test blocks were recovered and examined for changes in weight and for bacterial attack of lignified wood cell walls. Only small weight losses occurred. Scanning electron microscopy studies revealed that there was extensive superficial bacterial erosion of beech wood cell walls. The decay patterns are illustrated by micrographs and discussed in relation to other types of bacterial attack.

SPE Member ABSTRACT. Sulphide souring of the Ninian oilfield reservoir was studied to ascertain the possible involvement of sulphate-reducing bacteria in this important phenomenon. The data presented in this paper phenomenon. The data presented in this paper demonstrate the presence and growth of thermophilic sulphide generating bacteria throughout this facility. A range of bacteria were detected in representative water samples from close to the injection wellbore. These bacteria included mesophilic sulphate-reducing bacteria (m-SRB), capable of growth between 20 deg. C and 40 deg. C and thermophilic SRB (t-SRB), capable of growth between 50 deg. C and 70 deg. C. Thermophilic SRB were also found throughout the oil production system, in both water and surface film samples. The presence of t-SRB in the water cut from the oil producing wellheads suggests that a significant proportion of reservoir souring in this case may be bacterial in origin. Between 1984 and 1986, a number of microbiological surveys were carried out on the Ninian Field, initially to monitor the growth of SRB around injection wellbores. These surveys clearly showed that SRB were present in the formation close to the perforations of injection wells and that extended perforations of injection wells and that extended biocide treatment of 20 days continuous dosage was effective in reducing the numbers of these SRB. in addition there was an apparent reduction in hydrogen sulphide (H S) concentrations measured in injection well backflow samples. This reduction in H S could be caused either by cidal action against SRB or by the known H S scavenging properties of the glutaraldehyde based biocide. There was thus indirect evidence that bacteria were generating at least some of the observed H S in the reservoir. More recent studies have detected t-SRB in produced fluids from the producing wellheads and throughout the production system. This new evidence of t-SRB activity in the formations and their detection in hot oil production systems, has clear implications and ramifications for H S induced corrosion and cracking and on hydrocarbon handling operations. The field and laboratory evidence indicates that the previously unrecorded t-SRB have a wide temperature previously unrecorded t-SRB have a wide temperature and nutritional range. They are able to produce sulphide under the temperature and carbon source conditions of the oil formation. A simple model for bacterial colonization and growth in oilfield reservoirs is presented, together with a discussion of the implications for remedial measures to control microbiological growth. The core of this model is that seawater flooding completes the balance of sulfate, temperature and organic nutrient status in the reservoir. This favours the growth of t-SRB at a considerable distance from the injection well perforations. Such widespread microbiological perforations. Such widespread microbiological growth indicates that souring control by organic biocide application would be difficult to achieve, and this is supported by the results of laboratory biocide trials. The model predicts that a finite concentration of sulphide can be produced by this mechanism. Bacterial sulphide generation is limited by both nutrient source availability and sulphide toxicity. In the case of the Ninian Field, laboratory data and theoretical assessments indicate that sulphide toxicity would inhibit bacterial activity above approximately 100ppm dissolved sulphide. P. 301