tailieunhanh - Water Pollution Control - A Guide to the Use of Water Quality_1

Tại các khu vực đô thị hoá, khả năng xâm nhập địa phương của đất là không đủ, thường là để hấp thụ phóng điện cao điểm của nước mưa. Dòng chảy lớn thường phải được vận chuyển trong thời gian ngắn (2-10 phút) trên một khoảng cách dài (500-5,000 m). | In urbanised areas the local infiltration capacity of the soil is not sufficient usually to absorb peak discharges of storm water. Large flows often have to be transported in short periods 20-100 minutes over long distances 500-5 000 m . Drainage cost is determined to a large extent by the actual flow rate of the moment and therefore retention in reservoirs to dampen peak flows allows the use of smaller conduits thereby reducing drainage cost per surface area. In tropical countries peak flow reduction by infiltration may not be feasible because the peak flows can by far exceed the local infiltration capacities. Box Calculation of pollution charges based on population equivalents Calculation of the financial charges for industrial pollution in the Netherlands is based on standard population equivalents pe _ _ Q x COD peload of industrial discharge where Q wastewater flow rate m3 d 1 COD 24 h-flow proportional COD concentration mg COD l-1 TKN 24 h-flow proportional Kjeldahl-N concentration mg N l-1 136 waste load of one domestic polluter 136 g O2-consuming substances per day and by definition set at one population equivalent. Heavy metal discharges are charged separately Each 100 g Hg or Cd per day are equivalent to l pe. Each 1 kg of total other metal per day As Cr Cu Pb Ni Ag Zn is equivalent to 1 pe. An annual charge of US 25-50 1994 is levied per population equivalent by the local Water Pollution Control Board the charge is region specific and relates to the Board s overall annual expenses. Separate and combined sewerage In separate conveyance systems storm water and sewage are conveyed in separate drains and sanitary sewers respectively. Combined sewerage systems carry sewage and storm water in the same conduit. Sanitary and combined sewers are closed in order to reduce public health risks. Separate systems require investment in and operation and maintenance of two networks. However they allow the design of the sanitary sewer and the treatment