Suchergebnisse

published_or_final_version ; Environmental Management ; Master ; Master of Science in Environmental Management

ABSTRACTThe town of Driffield (in the East Riding of Yorkshire) has several combined‐sewer overflows which cause nuisance during rainfall. A new interceptor sewer has been laid and the sewage‐treatment works has been reconstructed to improve the water quality in the receiving watercourse. The sewerage scheme was mainly constructed using trenchless technology to reduce the risk of ground settlement in the narrow streets and to avoid contamination of the underlying aquifer. The existing biological filters were replaced with a new four‐basin cyclic activated‐sludge plant. This process achieves biological treatment within a single reactor basin which operates typically on six 4‐h cycles per day and without the need for separate primary and final settlement tanks.

AbstractTraditionally, sewage‐works design in Hungary has been based on rigid national standards with little consideration being given to the requirements of individual situations. This has resulted in plants that performed poorly and were expensive to construct and operate.The paper describes measures to improve the environment by upgrading Miskolc sewage‐treatment works, and the conflict between the cost of those facilities, and the ability to pay against a background of changing economic conditions.

ABSTRACTIn the past five years sewage‐treatment systems, based on artificial reed beds, have created much interest in Europe. In the UK, reed bed treatment systems have attracted this interest because of their potential for producing cost‐effective treatment for small communities. In 1985 a UK coordinating group was established to produce an integrated research and development programme for evaluating the process.This paper briefly describes the principles lying behind reed bed treatment systems, and outlines the progress which has been made to January 1988. The results of performance from eight full‐scale and pilot‐scale systems are presented in detail.

ABSTRACTThis sewage‐treatment works, which is located within the Lake District National Park, on the shores of England's largest lake, receives flows from the villages of Windermere, Bowness and Troutbeck and serves a population which can double from winter to summer.The paper describes the logistical and other aspects of undertaking construction works within the confines of an existing site whilst maintaining treatment to incoming flows. The background and regulatory influences on the design of the scheme are covered, together with details of the new treatment units and the provision of facilities to strip phosphate from the effluent.

ABSTRACTActivated SLUDGE SEWAGE treatment processes are often inadequate to comply with effluent criteria as promulgated in anti‐pollution legislation. Ozonation was studied as a means of improving nutrient removal activated sludge processes without the salinity and other disadvantages of the often used polyvalent metal salt addition. Direct ozonation into the aeration basin of a 150 I/d Phoredox (modified Bardenpho) system led to improved removal of organic substances. Nitrification was improved while phosphate removal was not adversely affected. Beneficial biological activity in the activated sludge was enhanced. The trihalomethane formation potential was reduced. Pollutional loads could be lessened, while an effluent with increased reuse potential was produced.

AbstractBrisbane City Council provides sewage‐treatment facilities for a population of 800 000, together with industrial effluents having an organic loading equivalent to a further 600 000 people. Three projects are described to illustrate some of the different designs and operating parameters used in Brisbane, where the sewage temperatures range from 18°C to 29°C and stormwater is collected separately. The first project is a 400 000 population equivalent augmentation to a conventional activated‐sludge plant located at Luggage Point. The two other plants have to comply, inter alia, with an effluent standard of 10 mg/l for total nitrogen. This requirement, together with site constraints and an economic evaluation of alternatives, resulted in the selection of the extended‐aeration process incorporating anoxic zones and separate mixing and aeration. These contemporary designs are specific to Brisbane conditions, and are intended to facilitate reliable operation as well as being cost effective.

ABSTRACTThe design of septic tanks, constructed wetlands, waste‐stabilisation ponds and rock filters is detailed, and their applicability in the UK is discussed. Septic tanks are a suitable primary treatment system for villages with a population of less than 500. Constructed wetlands, which are secondary or tertiary treatment units, have the disadvantage that their plants do not play any significant role in their performance, except for nitrogen removal. Secondary facultative waste‐stabilisation ponds, with pre‐treatment in septic tanks and post‐treatment in rock filters, provide primary, secondary and tertiary treatment and can produce high‐quality effluents. The costs of these processes for small rural communities in the UK are compared.

ABSTRACTThis paper describes experiments which were carried out on a high‐rate secondary‐treatment plant which incorporate a moving‐bed biofilm and floating filter. The same cylindrically shaped plastic elements were used both as a biofilm carrier and as a filter medium in the floating filter.

ABSTRACTOsaka has nearly completed its sewerage system, and twelve sewage‐treatment works are now in operation. Tsumori and Ebie works, the two oldest, were commissioned in 1940. For these works, full‐scale reconstruction has just commenced.This paper reports on the reconstruction of the Tsumori works, and outlines the plan for future reconstruction of the city's sewage‐treatment works.

AbstractThe process control of sewage‐treatment plants is normally carried out by conventional means. Special circumstances forced the application of a state‐of‐the‐art process automation system for The Netherlands'largest sewage‐treatment plant (Houtrust) at The Hague.The plant incorporates the use of oxygen‐enriched air for use in the secondary treatment process, and the final settling tanks are constructed one above the other (in two tiers). The automation system is built up with locally‐placed process computers, and a central video operating system is included with a data‐processing computer; these are interconnected by a data transmission bus of redundant design. The central control system is also connected to the main sewage pumping stations of The Hague district, for collecting data and controlling these stations from the plant.After the start‐up of the plant, it took several months of tuning the control system to gain proper process control, the main problem being the influence of pump switching in the intermediate pumping stations on the oxygen supply to the aeration tanks.

The combination of anaerobic pre-treatment and conventional aerobic technologies in a single compact unit has the potential to afford practical, sustainable and low-cost systems for the decentralized treatment of sewage. The aims of the present study were (i) to determine the efficiencies of a single-family compact (SFC) and a multi-family compact (MFC) station in removing organic matter from domestic sewage, and (ii) to investigate the behavior of aerobic intermittent sand filters (ISFs) regarding nitrification. The SFC station consisted of an upflow anaerobic sludge blanket reactor, an anaerobic upflow bed filter and an aerobic ISF, while the MFC station comprised a septic tank and two ISFs. The mean efficiencies for the removal of total chemical oxygen demand, total suspended solids and total Kjeldahl nitrogen were, respectively, 90, 93 and 75% for the SFC and 87, 91% and 74% for the MFC with ISFs operated at hydraulic loading rates of 380 L.m-2.day-1. The sand filters produced helminth-free effluents that complied with World Health Organization recommendations for water intended for agricultural reuse, although the geometric mean of E. coli counts (104 CFU.100 mL-1) was somewhat high, implying that the treated water was appropriate for irrigation in low-tech agriculture.

AbstractThis paper describes the operation of four prefabricated'package'biological filter plants which have been installed in Somerset by Wessex Water since 1984. Whilst these, in common with most other package sewage‐treatment plants, have advantages of low capital cost and minimum site requirement, some operational difficulties have arisen since commissioning, and effluent quality has been variable.This paper outlines the problems, and makes some suggestions for improvements.