2. Untreated municipal and industrial waste water
In Thailand, most of the natural waterways serve as sewerage for domestic and industrial waste water. A study in Bangkok Metropolitan Area estimated that 60–70% of domestic waste was discharged to the Chao Phraya River and eventually to the Gulf of Thailand without prior treatment. Table 1 and Fig. 1 show the BOD load from the major coastal zones of Thailand namely: central basin, eastern seaboard, eastern south and western south. The central basin contributes the highest BOD load with 34 376 t/year, of which 29 033 t/year are from domestic sources and 5343 t/year are industrial. These untreated wastes are discharged directly or indirectly to canals, rivers and sea, causing high BOD values and bacterial contamination close to populated and industrialized areas. This is because there are not enough waste water treatment facilities in the area.