Evaluation and Design Model of Decentralized Units for Wastewater Treatment

Abstract

Deterioration of the public health can be caused due to the discharge of untreated wastewater into the aquatic environment. Cesspits systems are the most common treatment units on household level in rural areas of Gaza Strip. The aims of this study were to evaluate the decentralized wastewater treatment plant inGazastrip, develop a mathematical model for optimum design of small wastewater treatment units and redesign of the existing units using the developed model. In this research, the available two local treatment systems were implemented by Palestinian Hydrology Group (PHG) and Palestinian Agricultural Relief Committees (PARC). They were studied to find out the weak points and then a mathematical model was developed to get the efficient design. The results show that by using the PHG system, the average removal rate of BOD and COD were 57% and 52% respectively while the removal rate of BOD and COD of PARC system were 75% and 57% respectively. The operators of both systems have ignored many essential factors as Boron, heavy metals CO3 and HCO3. It can be concluded that the improper design of both systems had negatively affected the treatment efficiency that influenced the natural growth of irrigated plants and the quality of irrigated soil. By using the developed mathematical model, many technical problems in the design were addressed and produced the proper design of both systems with results of BOD and COD removal compliant with local and international standards for reuse. Utilizing solar energy in heating wastewater was also investigated. An experiment was conducted to raise the temperature of wastewater by cycling heated water from solar system in copper pipes through the tanks to a considerable degree that increases the of treatment efficiency. The results presented in this thesis clearly demonstrate the big potential of this technology for the decentralized treatment of domestic wastewater in rural areas; nevertheless additional research work needs to be done, including an economic evaluation and the need to develop appropriate standards to be utilized for the design and construction of decentralized wastewater systems and also to promote realistic and acceptable standards for treated wastewater.