Chemical Characteristics 1. pH Value Extremes of pH: can adversely affect biological The pH shall be between 5.0 and 10.0 at all times. treatment processes can adversely affect the safety of operations and/or maintenance personnel cause corrosion of sewer structures increase the potential for the release of toxic gases such as H2S and HCN 2. Organic Strength BOD relates to the amount of oxygen required to treat or neutralise a Oxygen demand is measured by either Biological specified type of wastewater using a Oxygen Demand (BOD) or Chemical Oxygen Demand biological treatment. The NZ Standard (COD). 9201 recommends an acceptable BOD BOD is the preferred measure for tradewaste maximum of 1000 mg/L. A BOD restriction may be related to mass limits. Recently the method for COD The following limits have been set determination has been amended so that a less toxic catalyst is used. Therefore, the NZ Standard 9201 comments on toxicity are no longer relevant. Investigations on Seaview effluent since 1994 and a literature review establish that the ratio of BOD:COD is a relative constant for domestic sewage at 1:2.5 Organic Strength – Biological Oxygen Demand BOD Mass limits 2,000 mg/sec Organic Strength - Chemical Oxygen Demand COD Mass limits 5,000 mg/sec this may be expressed as: COD Composite limits (equivalent to these examples) 2,500 mg/L @ 2L/s 5,000 mg/L @ 1L/s 3. Inhibitory Chemicals No waste, whether or not diluted with wastewater, may inhibit the performance of the wastewater treatment process such that the Council is significantly at risk of or prevented from complying with its resource consent. 4. Maximum Concentrations The maximum concentrations permissible for the chemical characteristics of an acceptable discharge are set out in the following tables: Page 18