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The effect of sand filter media thickness on the performance of faecal sludge (FS) drying beds was determined in terms of: dewatering time, contaminant load removal efficiency, solids generation rate, nutrient content and helminth eggs viability in the dried sludge. A mixture of ventilated improved pit latrine sludge and septage in the ratio 1:2 was dewatered using three pilot-scale sludge drying beds with sand media thicknesses of 150, 250 and 350 mm. Five dewatering cycles were conducted and monitored for each drying bed. Although the 150 mm filter had the shortest average dewatering time of 3.65 days followed by 250 mm and 350 mm filters with 3.83 and 4.02 days, respectively, there was no significant difference (p > 0.05) attributable to filter media thickness configurations. However, there was a significant difference for the percolate contaminant loads in the removal and recovery efficiency of suspended solids, total solids, total volatile solids, nitrogen species, total phosphorus, chemical oxygen demand, dissolved chemical oxygen demand and biochemical oxygen demand, with the highest removal efficiency for each parameter achieved by the 350 mm filter. There were also significant differences in the nutrient content (NPK) and helminth eggs viability of the solids generated by the tested filters. Filtering media configurations similar to 350 mm have the greatest potential for optimising nutrient recovery from FS.

A treatment process to polish the biologically treated, secondary effluent from a newsprint mill in order to achieve wastewater recycle, has been investigated at pilot-scale. The polishing process included chemical coagulation and solids separation as the tertiary treatment for residual organic removal, and applied electrodialysis reversal (EDR) as the deep treatment stage for desalination. The chemical coagulation stage reduced total oxygen consumption (TOC), colour, and lignins by 81%, 81%, and 78% respectively. Those organics which were inert to biodegradation and resisted chemical coagulation, were reduced by half in the EDR plant. EDR reduced conductivity by 73% from 1800 uS cm -1 to 500 uS cm -1 . TOC was reduced by 90% to a level of 8 mg I -1 in this polishing process. The trial demonstrated a satisfactory plant performance and the EDR ion-exchange membrane showed a good fouling resistance. The quality of the final product was as good as, or better than, that of the fresh water supply on site. The running costs of the process were estimated at £ 0.23 m -3 , which makes it an economical and viable solution to further reduce mill water consumption, especially for those modem mills which already achieve a low water usage.

The International Association on Water Quality (IAWQ) Activated Sludge Model No.1 was used to optimise a full-scale activated sludge plant, treating a high-strength pulp and paper mill effluent operating at a temperature of 38°C. The model was calibrated by determining the mixing characteristics of the reactor and the oxygenation capactity of the aeration system in situ. In addition batch tests were carried out to determine wastewater COD fractions together with the important kinetic parameters necessary to run the IAWQ Model. Steady-state simulations carried out using the calibrated model were in good agreement with average plant operational data. As a result of major modifications which were undertaken to the paper mill white water systems, the investigation was repeated and the results revealed that both the wastewater characteristics and process kinetic features had changed and this was mirrored by changes in plant performance. Again simulations carried out using the revised parameters showed good agreement with plant operating data. As a result the model was used to provide recommendations for optimising plant operation, namely that by reducing sludge age, there would be a reduced oxygen consumption together with an enhanced COD removal. The model proved to be a valuable tool for predicting the steady-state performance of this activated sludge system treating pulp and paper mill effluent at elevated temperatures.

In an attempt to achieve water of a quality suitable for in-house re-use, chemical coagulation, ozone and activated carbon adsorption were investigated as options to remove both non-biodegradable COD and colour from the effluent of an activated sludge plant treating papermill waste water. Chemical coagulation was investigated using jartests and the results were scaled-up to a 6 m3 hr−1 pilot plant. This was able to remove 70% of the COD and 90% of colour using alum and it produced an effluent with a COD of 50 mg l−1 and colour of 40 Pt-Co units. Ozone dosed at 60 mgO3 l−1 could remove 90% of the colour but had a poor COD reduction. Isotherm tests of activated carbon adsorption showed a very high removal efficiency at 1.18 kg activated carbon m−3 product, but this dosage incurred an excessive cost. Chemical coagulation followed by dissolved air flotation (DAF) and multimedia filtration proved the most suitable tertiary treatment process train. Operating conditions were optimised for the chemicals applied, ...

In order to determine the potential indicator value of protozoa and metazoa for control of sequencing batch reactors, mixed liquor solids were examined microscopically for 200 complete cycles from start-up; a total of 100 days. Over the first 40 cycles a healthy, diverse, protozoal population was established which comprised free-swimming, crawling and attached ciliates. During this period the reactor demonstrated efficient removal of COD and suspended solids but did not nitrifiy. With the onset of complete nitrification there was a drastic change in microfauna which became dominated by flagellated protozoa. At around the 80th cycle rotifers appeared and at cycle 100 attached ciliates became the dominant group. The protozoal composition of the mixed liquor responded to reactor shocks such as pH variations and was shown to be a good indicator of the nitrification efficiency of the reactor.

The applicability of an advanced settler model is described for the removal of fibres from pulp and paper wastes by settlement. The model is based on flux theory and describes a settlement tank as 10 horizontal layers, with a mass - balance calculated for each layer. Using a pilot - scale settler of 1.42 m2 surface area, a 5 month experimental study was carried out to validated the model. The model was verified under both a quasi steady - state and under two dynamic events. Computer simulations suggested that the model will be useful for both design and operation of settlers handling liquid wastes from the pulp and paper industry.

From the middle ages until the early part of the nineteenth century the streets of European cities were foul with excrement and filth to the extent that aristocrats often held a clove-studded orange to their nostrils in order to tolerate the atmosphere. The introduction in about 1800 of water-carriage systems of sewage disposal merely transferred the filth from the streets to the rivers. The problem was intensified in Britain by the coming of the Industrial Revolution and establishment of factories on the banks of the rivers where water was freely available for power, process manufacturing and the disposal of effluents. As a consequence the quality of most rivers deteriorated to the extent that they were unable to support fish life and in many cases were little more than open sewers. This was followed by a period of slow recovery, such that today most of these rivers have been cleaned with many having good fish stocks and some even supporting salmon. This recovery has not been easy nor has it been cheap. It has been based on the application of good engineering supported by the passing and enforcement of necessary legislation and the development of suitable institutional capacity to finance, design, construct, maintain and operate the required sewerage and sewage treatment systems. Such institutional and technical systems not only include the disposal of domestic sewage but also provisions for the treatment and disposal of industrial wastewaters and for the integrated management of river systems. Over the years a number of institutional arrangements and models have been tried, some successful other less so. Although there is no universally applicable approach to improving the aquatic environment, many of the experiences encountered by the so-called developed world can be learned by developing nations currently attempting to rectify their own aquatic pollution problems. Some of these lessons have already been discussed by the authors including some dangers of copying standards from the developed world. The objective of this paper is to trace the steps taken over many years in the UK to develop methods and systems to protect and preserve the aquatic environment and from the lessons learned to highlight what is considered to be an appropriate and sustainable approach for industrialising nations. Such an approach involves setting of realistic and attainable standards, providing appropriate and affordable treatment to meet these standards, establishment of the necessary regulatory framework to ensure enforcement of the standards and provision of the necessary financial capabilities to guarantee successful and continued operation of treatment facilities.

Davyhulme sewage-treatment works, which serves the Manchester drainage area, is one of the lagest in the UK. The dry-weather flow is 300 000 m3/d, and the plant receives a wide range of industrial effluents. The works has been identified as a major source of pollution in the Mersey estuary, with an average discharge of 6500 kg ammonia/day. As part of its initiative to improve the Mersey estuary, North West Water intends to reduce the daily ammonia load from Davyhulme to about 1000 kg/d by 1995. In order to assess the capabilities of both conventional and novel processes to achieve this degree of ammonia removal, a number of on-site pilot plants were established. This paper reports on the pilot-plant studies and the selection of process options. Recommendations with regard to design parameters and final process selection are given.

The activated sludge process is commonly used for secondary wastewater treatment worldwide. This process is capable of achieving high quality effluent. However it has the reputation of being difficult to operate because of its poorly understood biological behaviour, variability of input flows and the need to incorporate qualitative data. To augment this incomplete knowledge with experience, knowledge-based systems were introduced in the 1980s however they didn't receive much popularity. This paper presents the Activated Sludge Expert system (ASExpert), which is a rule-based expert system plus a complete database tool proposed for use in activated sludge plants. The paper focuses on presenting the system's main features and capabilities to revive the interest in knowledge-based systems as a reliable means for monitoring plants. Then it presents the methodology adopted for ASExpert validation along with an assessment of testing results. Finally it concludes that expert systems technology has proved its importance for enhancing performance, especially if in the future it is integrated to a modern control system.

A rapid and simple procedure for the enumeration of faecal coliform bacteria present on the fingertips is described. The distribution of individual faecal coliform fingertip counts within households has been compared with a number of variables related to the availability of water supply and sanitation facilities. This showed a strong association between the fingertip count and the possession of in-house water connections. It is proposed that this test might provide a reliable indication of the effectiveness of certain public health interventions.