The comparison of deep sea outfall systems and wastewater treatment systems with samples of İstanbul

ABSTRACT It is known that as the capacity of treatment plant increases the unit cost of operation decreases. For this reason it is more economical to collect and treat the wastewater at one place as it is possible. However, to collect wastewater at one place depends on distribution of population and topographical form of the housing area. The electricity consumption of main pumps could be accepted as 4,2 watt-h/1 m3 wastewater (ww)-l m. As Mechanical Treatment Plants with Deep Sea Outfall Systems has less mechanical equipment than Biological and Advanced Biological Treatment Plants, being no process that needs expert personnel and if no high capacity main pumps, they can be operated without any engineers. However, one or two engineers should be employed in high capacity plants that wastewater has to pumped. 24-34 personnel including 2 engineers are enough for operation of the mechanical treatment plants with capacity of 350,000-400,000 mVd and have pumps for 15 m height. The electricity consumption of mechanical treatment consists of coarse screen, fine screen and aerated grit chamber can be said 3.7 watt-h/m3. The unit operation cost of a mechanical treatment plant with 350,000-500,000 m3/d will be 0.0043-0.0047 $/m3-ww and the unit cost of a mechanical treatment plant with odour removal by ozone without Odour Control Unit will be between 0.0047-0.0051 $/m3-ww. The unit operation cost of mechanical treatment plants with odour control by ozone will be nearly 0.0075 $/m3-ww. The operation and the unit operation cost of mechanical treatment plants with odour control by ozone with capacity of 300,000-500,000 m3/d can be calculated as follows: Total operation cost ($/month) = 0.0075. Q + [4.2. Q. H. (YTL/kw-h). ($/YTL) ] (also pumping cost if pumping exists) Unit operation cost ($/m3) = 0.0075 + [4.2. Q. (YTL/kw-h). ($/YTL) ] (also pumping cost if pumping exists) Q : Wastewater flow rate (m3/month) H : Pumping head including head loss (m) A biological or advanced biological wastewater treatment plants are operated according to their capacity. A plant with 60,000 m3/d capacity is operated with 70 persons including 9 engineers, a plant with 230,000 m3/d capacity is operated with 80 persons including 9 engineers and a plant with 665,000 m3/d capacity is operated with 125 persons including 9 engineers. In the wastewater treatment plants in which sludge is produced and sludge dewatering unit exists (3 plants), in the case of discharging sludge to dewatering unit that solid matter (SM) content more than %4, to get sludge cake with high SM content (> 25%) and low concentrate supernatant, it is determined that optimum polyelectrolyte amount is 3 kg-poly/ 1 tonne dry solid matter. xinThe average unit cost of electricity consumption can be taken as 0.0117 $/m3 - ww for biological wastewater treatment systems and the average unit cost of electricity consumption can be taken as 0.034 $/m3 - ww for advanced biological wastewater treatment systems. The unit operation cost for 60,000 m3/d capacity plant would be 0.081 $/m3-ww, 0.029 $/m3-ww for 230,000 m3/d capacity and 0.013 $/m3-ww for 665,000 m3/d capacity (electricity cost for pumping and energy production from gas are not included). The unit electricity consumption for biological wastewater treatment plants can be taken 110 watt/m3-ww 450-550 kw-h/tonne-BOIs and the unit electricity consumption for advanced biological wastewater treatment plants can be taken 320 watt/m3-ww 1480 kw-h/tonne-BOIs. The total unit cost of operation increases 16.1% from 0.1145 $/m3-ww to 0.1329 $/m3-ww by 40 m pumping in Paşaköy Advanced Biological treatment Plant. The total unit cost of operation increases 20.5% from 0.0407 $/m3-ww to 0.0493 $/m3-ww by 18 m pumping in Tuzla Biological Treatment Plant. The total unit cost of operation also decreases 44.3% from 0.0244 $/m3-ww to 0.0136 $/m3-ww by electricity production from gas in ASKİ Biological Treatment Plant. The operation cost of Paşaköy Advanced Biological Treatment Plant is very high, because of high pumping height and electricity cost for additional oxygen requirement for nitrification process besides the biological treatment plants only for carbon removal. As high sludge retention time, significant amount of the organic part is oxidized by endogenous respiration and in advanced biological treatment plants (nutrient removal systems) the methane produced by sludge digestion is less than in biological treatment plants for only carbon removal by active sludge process. For these reasons, the amount of produced gas per removed organic matter in treatment plants for nutrient removal with advanced biological system should be investigated if it is worth or not for such an investment and the economical analysis of nutrient removal by different processes after biological treatment for only carbon removal to benefit from organic part of wastewater could be studied. As ASKİ Biological Treatment Plant has no main pumping station and nearly 90% of the electric consumption is covered by gas production, its unit operation cost decreases nearly the unit operation cost of Mechanical Treatment Plants with Deep Sea Outfall Systems in Istanbul (according to two examined plants) which have 14-15 m pumping head. The cost of electricity is 41% of total cost in Tuzla Biological Wastewater Treatment Plant. For this reason by equipping the system that convert the anaerobic digester gas to electricity, the operation cost will decrease in good operation conditions. Mechanical Treatment Plants with Deep Sea Outfall Systems' investment and operation cost related to capacity is more economical than biological and advanced biological treatment systems' cost. Key words: Mechanical Treatment Plants with Deep Sea Outfall Systems, Paşaköy Advanced Biological Treatment Plant, Tuzla Biological Treatment Plant, ASKİ Biological Treatment Plant, unit operation cost, unit cost of electricity consumption, total unit operation cost. xiv