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Mamloo Dam is under construction downstream of the Jajrood River to supply Varamin plain's irrigation water, flood control and produce energy.The river water quality as DO, BOD and temperature and its self-purification capacity was studied to define the minimum safe water flow downstream of the dam.The results show that the water quality will not change considerable upstream of the Parchin complex. However, after the complex outfall, the river water quality changes severely; even the effluent is treated up to National standard levels.The main reasons for the changes in river water quality are Parchin high water withdrawal as well as the high ratio of its effluent to the river flow. The dam construction will raise this effect significantly.The results show that national effluent standards, which are based on pollution concentration without considering waste loads and receiving environmental conditions in some cases cannot be satisfied and promulgation and enforcement of effluent standards are necessary.

Birjand is a city in the east of Iran. Underground water is the only drinking water source, because this city is in a dry region.Ground water hexavalent chromium ion (Cr +6 ) concentration in Birjand is about 0.07 mg/l, which is higher than the maximum contamination level (MCL). The maximum contamination level of Cr +6 is 0.05 mg/l according to WHO guidelines.In an effort to comply with the World Health Organization (WHO) guideline regulations governing hexavalent chromium, Cr +6 was reduced to Cr 3 through standard jar test procedures with the addition of ferrous sulphate as a reducing agent. This research studied this as a bench scale.In the first alternative, ferrous sulphate was just used as a reducing agent. A chromium concentration of 0.042 mg/l was reached in order to comply with WHO guidelines. But the addition of ferrous sulphate induced a sulphate ion (SO 4 2-) concentration increment of up to 430 mg/l, which is higher than the maximum contamination level according WHO guidelines (400 mg/l).In the second alternative, ferrous sulphate was used as a reducing agent with lime milk.A chromium concentration of 0.015 mg/l was reached with a sulphate ion concentration of 380 mg/l, which is less than the MCL (400 mg/l).

In drinking water treatment, prechlorination and preozonation are often applied in order to control micro-organisms and taste and odour causing materials, which may influence organics removal by pre-oxidation and adsorption.Using commercial and natural water humid substances, the positive effect of prechlorination and preozonation as an aid to coagulation-flocculation of these compounds were confirmed by the removal of total organic carbon (TOC). These experiments were conducted at bench-scale through a series of jar tests using different pH, coagulant dosage and TOC concentration of approx. 4, 8 and 12 mg/l. In addition to TOC removal, the existence of an optimum preozonation dose and an optimum prechlorination dose were also confirmed. Experiments show that prechlorination and preozonation can improve coagulation and flocculation depended on TOC concentration of influent surface raw water. The results demonstrate a differential effect between prechlorination and preozonation on removal of TOC. Preozonation showed a positive effect on a system with low influent TOC and very low molecular weight (noncolloidal) humic substances.

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