Settleable substances

It is necessary to determine the settleable substances immediately after the sample is taken in order to avoid the secondary formation of deposits in the water sample during transport. The volume of the settleable substances, or their mass, is increased for example by oxidation processes in the presence of air which cause the oxidation of such elements as dissolved iron. This secondary reaction causes an increase in the settleable substances. For a number of years the method using an Imhoff sediment cone has proved valuable in the determination of settleable substances. This method 

Imhoff sediment cone is used, as shown in the diagram below. 

The sediment cone holds a volume of 1 litre of water. It is conical in shape and the lower part is graduated. The quantity of water under investigation is transferred to the sediment cone immediately after sampling and left for 2 hours. During this settling time of 2 hours, the sediment cone should be turned sharply, for example every 30 minutes. This procedure is intended to cause the sedimentation of settleable substances adhering to 

If the settleable substances are also to be determined by weight, a water sample, taken in the same way, should be filtered locally through a weighed paper filter contained for transport in a Petri dish. The filter should 

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Analysis of sewage. In the routine analyses used to analyze sewage, processes to determine temperature, pH, settleable substances, chemical oxygen demand and biochemical oxygen demand are usual. More comprehensive analyses of sewage also record organic substances such as oil and grease-type... 

If water samples contain settleable substances, it may be appropriate... 

Nevertheless, this must be regarded as a better solution than a single or multiple random sample. Production of time-proportional composite samples is also possible, using automatic sampling devices where applicable. The composite samples can be taken with or without settleable substances. If the water contains many settleable substances, it is more favourable to remove these substances before producing the composite samples and to investigate them separately in the laboratory. After removing the settleable substances, the water from the composite samples should be used for laboratory tests. If secondary turbid substances have formed in the water, these should be included in analyses. 

The settleable substances should be determined immediately after sampling or after producing a composite sample, so that secondary precipitations during transport are not included in the record as settleable substances. It is also useful to measure the following physico-chemical parameters of individual samples on site ... 

Settleable substances in terms of volume are determined directly after sampling in a sedimentation funnel. If settleable substances are to be recorded in terms of weight, the water should be filtered via a membrane... 

Settleable substances" (suspended, deposited or floating substances) are principally determined using the volumetric method (see drawing in Chapter 1). 

Wastewater treatment systems can be classified, in addition to pretreatment, as preliminary, primary, secondary, and tertiary (advanced) treatments. Pretreatment of industrial wastewater is required to prevent adverse effects on the municipal wastewater treatment plants. Preliminary treatment is considered as any physical or chemical process that precedes primary treatment. The preliminary treatment processes may consist of influent screening and grit removal. Its function is mainly to protect subsequent treatment units and to minimize operational problems. Primary treatment is defined as the physical or chemical treatment for the removal of settleable and floatable materials. The screened, degritted raw wastewater from preliminary treatment flows to the primary clarification tanks, which are part of the primary treatment facilities. Secondary wastewater treatment is the process that uses biological and chemical treatment to accomplish substantial removal of dissolved organics and colloidal materials. The secondary treatment facilities may be comprised of biological reactor and secondary clarification basins. Tertiary (advanced) wastewater treatment is used to achieve pollutant reductions by methods other than those used in primary and secondary treatments. The objective of tertiary wastewater treatment is to improve the overall removal of suspended solids, organic matter, dissolved solids, toxic substances, and nutrients. 

Suspended, deposited and/or floating substances which are settleable or may be filtered off under defined conditions. 

If the biochemical oxygen demand of the settleable solids is to be determined, it may in the case of primary sludge be calculated from the loss on ignition of the settleable solids. According to Imhoff, 30 g organic substances cause 20 g BOD5 in primary sludge. 

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