Trade Waste/Wastewater

Wastewater Parameters

Wastewater samples are routinely analysed for process control purposes in wastewater treatment plants. Similarly trade waste samples from industrial activities are analysed to ensure compliance with discharge permits. A number of environmental licences (eg linked to wineries and dairies) require periodic sampling and testing of samples to ensure compliance. All tests specified in such licences can be performed at AWQC.

Test include several mentioned above such as BOD and COD but also Cyanide, Phenol (total), MBAS (anionic surfactants), Sulphides, Alkalinity (sludges), Chlorine residuals, UV absorbance and Oil and Grease. Various measurements of solids are available including total dissolved (TDS, derived from conductivity but also by evaporation), suspended (SS), volatile suspended (VSS) and total (TS) and volatile solids (VS).

Biochemical Oxygen Demand (BOD) is usually defined at the amount of oxygen required by bacteria while stabilising the decomposable organic matter under aerobic conditions. What this means in practice is that the BOD test is widely used to determine the pollutional strength of domestic and industrial wastes in terms of the oxygen that they will consume if those wastes are discharged into natural watercourses. Also the changes in BOD as waste water passes through a wastewater treatment plant are used as a guide to that plant's efficiency and to pinpoint potential trouble spots.

Like BOD, Chemical Oxygen Demand (COD) is also used a means of measuring the organic strength of wastewaters. The test relies on the oxidation of organic matter by a strong oxidising agent under acidic conditions. Thus COD measurements will always be greater than BOD measurements and the difference is linked to the biodegradability of the organic matter present in the sample. For example, the COD of a wastewater from a wood pulping waste will be significantly higher than the BOD because there is a significant amount of non-biodegradable material present.

There are various types of solids that can be measured. The usual definition refers to material that remains after drying. This material consists of two components; one being dissolved material made up mainly of inorganic salts but also potentially dissolved gases and some organic material and the other, undissolved material is referred to as suspended solids (SS), suspended matter or sometimes non-filterable residue. The filterable residue can also be determined and is known as total dissolved salts by evaporation.

The other useful solids tests are to carry out Total and Volatile Solids analysis on sludge samples to estimate the amount of organic matter present. By first drying a sludge sample and then combusting the sample at 550oC, an estimate of the inorganic (ash) and the organic (volatile) fractions of the total solids can be determined.

Wastewater samples, particularly those sourced from industrial sites are often analysed for cyanide (from plating baths), phenols and MBAS (anionic surfactants or "detergent").

Oil and Grease (or just grease) content of wastes is an important consideration in the handling and treatment of these materials for ultimate disposal. Often, the amount of grease that can be disposed of into a sewerage system will be carefully controlled through the use of a trade waste permit.