Industrial contributions constitute as much as 20% of the 700 000 m3 .d−1 of sewage discharged to the Saronikos gulf through the sewerage system which serves the Greater Athens area. The main industrial discharges originate from food, textile, pulp and paper, chemical, tanning and metal processing and electrical industries. In the majority of the cases the pretreatment is inadequate and the existing emission standards are violated. This results in increased concentrations of toxic metals in the sewage. The impact of these toxic discharges on the marine environment and the sewage treatment works have been investigated. Increased concentrations in the water column and the sediments have been reported but there are no indications of accumulation of toxic metals in the body of benthic organisms. The impact on the imminent operation of the treatment works for the sewage of Athens, have been investigated with the aid of pilot and bench scale studies. The results did not indicate a serious inhibition of the sensitive digestion and nitrification processes. However due to the high concentrations of the heavy metals, with average values approaching threshold values, it is important that appropriate action is taken to control industrial discharges through a revised and rational regulatory framework.
Small scale activated sludge plants are used extensively in tourist areas for the treatment of wastewaters from hotels and other tourist establishments. A recent survey carried out in a big tourist island of Greece showed that the majority of small plants did not perform satisfactorily. The most important problems identified were associated with diurnal flow fluctuations, inadequate control of air supply and sludge return rates, accumulation of grease and fats in the plant and bad design. Another important problem appeared to be the lack of trained personnel for the operation and maintenance of the plant. These problems are discussed in detail and possible measures are presented. Experimental results from the monitoring of two small extended aeration plants confirmed the bad effect of sudden surges of flow on effluent quality. Moreover it was found that the time required for the startup of the plant was approximately six weeks.
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