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3.5 Disposal (Topic e)

Outfall discharges are the most common method of disposal of wastewater for communities located near a surface water body, such as a river, lake or ocean.

Nowadays the design of a new outfall generally requires detailed analysis of wastewater characteristics and applicable regulations and guidelines for wastewater discharge.

Of the wastewater from developed countries which is discharged to a river or the ocean, most will have undergone some form of treatment. The opposite is true in developing countries where only 5 - 10 % of wastewater will have been treated before discharge. It is transported by gravity sewer systems except in low ground level areas where it is transported by pressure sewers using booster pump stations. For all sewer types, pressure dosing by box sewers is being encouraged instead of concrete and gravity systems being used as open ditches and open channels.

Any treatment and disposal eventually returns the water to the water cycle, whether facilitated by infiltration basins, ocean discharge, river discharge, lake discharge, evapo-transpiration from irrigation areas (including the leach drain areas from septic tanks in backyards), ground water recharge to estuaries or other means.

It has been widely recognised that the problem of disposal of wastewater is primarily a matter of communal sanitation, and that the problem is greater in areas of dense population, where civilisation is more advanced, or areas of greater industrialisation.

Therefore there is a need to minimise the amount of contaminants flowing into and collecting in particular disposal areas.

Rapidly increasing municipal and industrial water demands in recent decades have caused dramatic increases in wastewater. Take the case of discharged wastewater during the period of 1985-1995 as an example. The total discharged amount of wastewater in China during that period increased by 100%. A small portion of the wastewater was treated and the remaining 80-90% of wastewater was directly discharged into rivers, lakes and other water bodies, resulting in serious pollution of surface water and groundwater around Chinese cities. In 78% of river sections that flow through cities, the raw water can not meet standards required of a water source for drinking water. Half of the surrounding ground water is polluted. This serious pollution of surface water and ground water resulted in the reduction of the water resource potential (Lin 1999).

Wastewater treatment facilities are inadequate in many cities of the Asian and Pacific Region. In many places, untreated household and industrial wastes are discharged directly into canals and rivers, often contaminating the drinking water supply and spreading disease. The People’s Republic of China, had over 200 million city dwellers in 1980, but only 35 small municipal wastewater treatment plants. As a result, up to 90 per cent of the estimated 37 billion cubic metres of sewerage discharges that year remained untreated. In Shanghai alone, only 4 per cent of the estimated 5 million cubic metres of wastewater was treated. In the same city, in 1979, 96 per cent of surface water samples collected were found to be contaminated with heavy metals. Such heavily polluted water could possibly be a contributor to the rapidly rising cancer morbidity and mortality rates in the People's Republic of China's industrial regions, although scientific evidence to support such a claim is not yet reported (ESCAP, 1993). This illustrates the scale of the problem for developing countries. The impacts attributed to water pollution in selected cities of the Asian and Pacific Region are summarised in Table 3.15.

In Indonesia, river water quality analysis has generated additional water quality results to supplement the existing data. The regional variation of BOD in some areas is wide, ranging from 10 to 255mg/l, and the BOD concentration exceeds 100 mg/l, at about half of the observation stations. The river water BOD in the wet season, however, declines to approximately half as much as in the dry season due to the dilution effects of increased river flow. Fecal coliform exceeds more than 106 (MPN/100ml) at almost all observation stations. This means that almost all river water is affected by human wastes to a great extent.

Sea water COD in Jakarta Bay ranges from 18 to 81 and averages 28 mg/l. This COD is composed mostly of soluble COD. Average fecal coliform of the Bay is estimated at 2,530 (MPN/100ml). The Bay, especially at its coastal area, is much affected by human waste.

Since the United Nations Water Conference in Asia, many countries of the Asian and Pacific Region have formulated national water policies and plans to regulate the ownership, use and protection of water resources.

In Vietnam there are numerous lakes, rivers and ponds within urban areas. These are used for drainage, flood control, recreational purposes, irrigation, aquatic culture and as receiving waters for wastewater. Hanoi has the largest proportion, with 15% of the city area as natural waters, but HCMC and Haiphong also have large water areas.

Municipal wastewater is discharged without treatment to rivers and lakes. The survey reported that the majority of households have flush toilets, indicating a high environmental standard. Unfortunately this may be deceiving, because most households discharge their septic tank effluent directly into the streets, drainage ditches or natural water bodies. A minority infiltrates the effluent into the ground, although this may vary from place to place according to the soil condition. There is a flagrant lack of environmental management and control with the disposal of wastewater from public as well as private sanitation facilities.

For example, the situation in Haiphong may only be representative for the Red River Delta, where the soil is clayey and not very suitable for ground infiltration, but according to the household Survey, 81 % of sullage from households is discharged to the streets. Among households with flush toilets and septic tanks, only 9% infiltrate the effluent into the ground, 67% discharge directly to the streets, while the remaining 24% to natural waters or wetland. It is not difficult to observe sewage and sullage flowing long distances along the gutters, mixing with the street garbage, in Haiphong.

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