P.G. Smith

Giardia cysts and Cryptosporidium oocysts at sewage treatment works in Scotland, UK.

Abstract A three year study on Cryptosporidium oocysts and Giardia cysts in sewage was conducted with emphasis upon: (1) development and assessment of techniques for sampling and processing sewage for these parasites; (2) a field study in which six sewage treatment works (STW) were assessed for removal of these parasites from the liquid phase; and (3) assessment of effect of sewage treatment on survival/destruction of Cryptosporidium oocysts. In sampling, grab samples were superior to filtered samples. In concentration and clarification of samples, the most efficient technique was that in which sample manipulation was minimised. Although calculated parasite removal efficiency varied for both parasites and between and within STW, some consistent patterns were observed. First, Giardia cyst removal was significantly greater than Cryptosporidium oocyst removal. Second, most parasite removal occurred during secondary treatments, rather than during primary settlement. Third, no significant difference between efficacy of activated sludge treatment and trickling filters at parasite removal was detected. Also, in one STW which utilised tertiary sewage treatment, most removal from the liquid phase occurred during preceding treatment stages. Finally, one STW had significantly higher removal efficiencies of both parasites than the other five STW investigated. Low numbers of viable oocysts were detected at both influent and effluent. Survival was monitored by introducing oocysts, in containers bounded by semi-permeable membranes, into various environments within one STW. The results demonstrated that, over one week, none of the environments tested had a deleterious effect on oocyst viability, with the exception of the sludge-holding tank. Results are discussed in relation to other published work on Cryptosporidium and Giardia in sewage and recommendations for further areas of research on this subject are made.

The influence of pH and coarse media on manganese precipitation from water

Abstract This technical note represents the initial results of a research project investigating manganese removal from water by filtration through low cost coarse media which may be suitable for rural water treatment in developing countries. A manganese solution of 1 mg/l was shaken with limestone, gravel, crushed brick or with no solid media at various pH values. At a final pH value of 8.5, limestone gave 95% removal of manganese, crushed brick gave 82% removal, gravel gave about 60% removal and the removal for aeration and settlement with no solid media was less than 15%. The results indicate that rough solid media and the presence of carbonate are beneficial in the precipitation of manganese in water.

Diffusivity, tortuosity and pore structure of activated sludge

Abstract This paper describes new techniques in studying and defining pore morphology of activated sludge. Diffusion measurements on activated sludge are carried out in a diffusion cell. The average diffusivity in activated sludge is found to be 7.4 × 10−10 m2 s−1. Surface area determinations are used to calculate the mean pore radius of activated sludge flocs. This value is found to be between 108 and 130 A. The tortuosity of the pores in activated sludge is also calculated and found to have an average value of 2.73.

Removal of manganese from water using crushed dolomite filtration technique

This paper discusses manganese removal from water by filtration through low cost coarse media. A laboratory scale filtration technique was used to remove manganese from manganese bearing water to prove previous batch studies which showed that the removal of manganese was better in the case of limestone particle as compared to the gravel, crushed brick or with no media addition, and the conclusion made that removal mechanisms were due to the effect of rough solid surfaces and the presence of carbonate in the limestone particle. Filtration results indicated that at an input pH of 7 with manganese concentration of 1 Mn/l, a good removal was observed in the limestone media as compared to the gravel media, which validates the batch results. Results also show that water hardness did not significantly increase in this filtration technique. Studies on the effect of different parameters on the removal performance of manganese has shown that a smaller particle size, a greater filter depth, and a lower flow rate gave advantages in the removal efficiency.

A method for determining specific surface area of activated sludge by dye adsorption

A new technique is discussed for measuring the surface area of activated sludge. The method is shown to be easy to perform and reproduceable. The results indicate that activated sludge is highly porous with a specific surface area of between 40–140 m2 g−1 dry solids.

Removal and destruction of intestinal parasitic protozoans by sewage treatment processes

This paper reviews the literature which addresses the occurrence of intestinal protozoan parasites in sewage as well as the removal and destruction of these pathogens in sewage treatment processes. The concentration of intestinal protozoa within sewage depends upon the catchment; the prevalence and intensity of human infection within the catchment; the contribution of animal waste to the sewage and the prevalence and intensity of animal infection within the catchment. Some research indicates that some sewage treatment processes may result in relatively high removal efficiencies of some intestinal protozoa, whereas other data indicate that the concentration of cysts and oocysts discharged in sewage effluent may be in the order of several thousand per litre. For some protozoan parasites, such as Cyclospora, Microsporidia and Isospora, knowledge is scarce on the potential importance of sewage in their transmission and their likely removal and destruction by sewage treatment processes.

Pesticides in groundwater in Britain

The maximum admissible concentration (MAC) stated by the Directive from the European Community is 0.1 μg 1‐1 for individual pesticides, and groundwaters with levels above this require treatment by law before being supplied for drinking purposes. However the 1980 Directive is the subject of debate due to its absence of a toxicological assessment. This paper discusses some of the arguments for setting MAC values for pesticides in drinking water. The pesticides that have been most frequently detected in groundwaters in England and Wales are the triazines namely simazine and atrazine. These pesticides are herbicides emanating from diffuse mainly non agricultural situations, for example weed control operations on industrial sites, railways and road edges. Although agricultural herbicides are used in much greater tonnages that the triazines, the former are only occasionally noted in groundwater samples.

The role of air bubbles in the desorption of ammonia from landfill leachates in high pH aerated lagoon

Desorption of NH3 from wastewater in a laboratory scale aerated lagoon was investigated. Landfill leachate of around 575 mg L−1 NH3-N was used as the wastewater. The pH was raised to above 11.0 to achieve almost 100 conversion of NH+4 to NH3. The study quantifies the percentage NH3 desorbed at the free liquid surface and that desorbed into the air bubbles. Theoretical calculations and practical observations showed that between 15 to 38% of the total NH3 that was lost could be accounted for by desorption into the air bubbles. The rest of the NH3 desorption was at the upper liquid surfaces. The main role of the air bubbles is to create surface turbulence; NH3 desorption into the bubbles is of secondary importance.

A model of localised oxygen sinks around bacterial colonies within activated sludge

Abstract A new mathematical analysis of diffusional resistances of oxygen in activated sludge is developed. It assumes that the distribution of bacteria within activated sludges flocs are in colonies rather than the usual assumption of a homogeneous distribution of bacteria throughout the sludge. The solutions are for steady-state. The bacterial colony model results in a completely different shape of dissolved oxygen gradient in the floc when compared to the homogeneous bacterial distribution model. The new “bacterial colony” model predicts highly localised oxygen demands around the colony with maximum dissolved oxygen deficits in a 20–40 μm dia floc of 2–3 mg l −1 .

Formation of manganese micro-nodules on water pipeline materials

A study was carried out on the interaction of a manganese oxidising bacterium growing as part of a biofilm on the surface of polyvinychloride (PVC) and high-density polyethylene (HDPE) pipe material. After 2 weeks the formation of micro-nodules was observed within the biofilm. The energy dispersive X-ray spectroscopy (EDS) analysis of these micro-nodules showed high manganese and oxygen levels and indicated the possible formation of a manganese oxide complex. The nodules were found to average 10 μm in diameter and most had a central hole of approximately 2μm.