Characterization and Treatment of Leachates from Hong Kong Landfill Sites

Development of a large landfill site in the North-Eastern New Territories of Hong Kong, which will receive 25 million m³ of wastes during a life of about 13 years, must include the provision of a scheme to manage leachates which will arise in the tropical climate of the region.
The paper presents detailed results from a study commissioned by the Environmental Protection Department of the Hong Kong Government, to characterize and treat leachates generated by landfills in Hong Kong, in order to design a suitable management scheme. Field and laboratory trials which were carried out during 1989 showed that, although leachates from Hong Kong landfills have some specific characteristics (e.g. concentrations of amm.N to 5000 mg/l), they can be treated to high standards by aerobic biological processes.
As a result of these studies, a scheme has been designed which will provide a high degree of environmental protection in respect of leachate, as the landfill is developed.     

Upgrading the Activated-Sludge Process for Total Nitrogen Removal in Hong Kong

In order to protect the sensitive waters in Tolo harbour (Hong Kong), Sha Tin and Tai Po sewage-treatment works were first designed to remove 70% of the nitrogen load from the sewage. Since then, due to continuing serious eutrophication problems in the harbour, both plants have been modified to increase the removal efficiency to 90%.
The modifications were based on the Bardenpho process. However, the designers of the two plants adopted different approaches to process intensity, complexity and control of bacterial foam. At Sha Tin, the average monthly results have shown an increase of total nitrogen removal from 60–70% to about 80% since its completion. The addition of methanol was found to be ineffective on further enhancement of the denitrification rate due to difficulties in the apportioning of the second anoxic zone. The overall monthly results for Tai Po have also shown an increase in the removal rate to about 80%, even though 90% was achieved for a short period of time. The major problem encountered at the latter plant was that the process design did not provide an effective control on bacterial foaming, which had affected the smooth operation of the process.     

Pilot Scale Aerobic Sequencing Batch Reactor for Pig Waste Treatment

A n existing aetated lagoon treating piggery waste was converted into an aerobic sequencing batch reactor (SBR). After the commissioning period, the SBR plant treated piggery wastewater containing BOD and suspended solids (SS) concentrations of 2881 mg/l and 1419 mg/1 respectively, producing an effluent having an average BOD and SS of 18.7 mg/1 and 12.3 mg/1 respectively. The volumetric loadings on the SBR and the process were similar. However, the SBR process operated at a lower mixed liquor suspended solids (MLSS) concentration and shorter sludge retention period. Although the capital and operating costs of the SBR are higher than for the aerated lagoon, the simplicity of operation, the high BOD and SS removal efficiency, and the small land requirement make this type of process an attractive treatment option, particularly in places where land supply is limited and expensive.     

GULLANE OUTFALLS, SCOTLAND

This paper describes design and construction of two new sea outfalls discharging from Gullane Waste Water Treatment Works (WwTW) to Aberlady Bay, on the south side of the Forth estuary (Firth of Forth), 25km east of Edinburgh, Scotland. The outfalls were installed by float and lower, using the Flow-Lay® technique, believed to be a first for steel pipes. The paper also describes air transport, beach movement and soil liquefaction and their effect on pipe stability, material and profile.     

TREATMENT OF WASHWATER FROM SERVICE-RESERVOIR CLEANING IN HONG KONG

As a result of increasing control of environmental pollution in Hong Kong. the practice of discharging untreated service-reservoir washwater to the nearest watercourse is no longer permitted. This paper describes the results of field tests on alternative methods of treating the effluents produced from cleaning fresh-water and sea-water service reservoirs in Hong Kong, including trials of alternative cleaning procedures using high-pressure jetting which were designed to (a) upgrade the cleaning efficiency and (b) reduce the resulting pollution load. The results of effluent treatment, based on pilot-plant trials incorporating various combinations of filtration and centrifugation, are presented. The option which was selected for full-scale implementation, based on a mobile centrifugation and microfiltration unit, using a membrane developed in China specifically for the water industry, is described     

Water Treatment – An Updated Hong Kong Experience

This paper discusses the recent development of water treatment in Hong Kong. A review is made of some major treatment works completed in the last decade, giving the design parameters, treatment methods and performance. The paper also addresses the environmental impact issues of liquid chlorine and sludge disposal pertaining to the design of water-treatment works.