rhouses, anaerobic systems seem to be appropriate wastewater purification systems. Simple anaerobic systems may achieve 50% of BOD-purification (Table 4), while high-rate anaerobic systems may result in 90% of BOD-purification (Table 5). Anaerobic systems do not remove such nutrients as ammonium-nitrogen. If liquid and slurry are used as fertilizer this does not need to pose specific problems. Nutrient removal systems should be applied only if water authorities set limits for the discharge of nutrients. As in most countries this is not the case, there are no reasons for industry to make high investment costs for tertiary treatment [20]. br/>
Table 5. General:
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The process that may be used for the treatment of wastewater produced by the industries mentioned in this report do not differ very much from each other. In general, these systems are applied to a large extent in developed countries. In developing countries adoption rates are much lower. Especially for these latter countries, treatment methodologies and technologies should be cheap, efficient and easy to operate. Important differences of wastewater treatment in the different industries will be mentioned [10]. Large dairies in many developing countries, treatment of wastewater is not even considered as an option. Because in developing countries the amount of milk processed industrially is minor, wastewater problems will mainly occur at the plant site and the surrounding surface waters. This implies that dairy wastewater problems in these countries are very local in contrast to those in developed countries. The dairy wastewater problem is larger in developed countries because all milk is processed industrially. For dairies in these countries it is very important that proper wastewater treatment system are installed [25]. Mentioned before, the primary action to reduce pollution by wastewater discharge, is efficient water management. After a thorough search for ways to reduce water use and wastewater production, the inevitable produced wastewater can be treated in different ways as discussed below [19]. Wastewater produced during the day has a variable composition. For the optimal performance of most treatment system it is necessary that the load is rather constant and that the plant is fed with a rather constant wastewater flow. Wastewater is therefore collected in equalization or balance tanks [32]. br/>
7.1 Most treatment plants follow the following steps
Preliminary treatment. This type of treatment includes screening, skimming and settling which can lead to the recovery of by-products, grease and fat and removal of coarse solids. For an optimal performance and to avoid overload of the screening devices, it is important that large amounts of produced solids such as (hog) hair, feathers etc. are collected during the processing itself. For developing countries, ...
