ABSTRACT
This study was carried out on the design and performance evaluation of a waste water treatment plant. This study was carried out on a wastewater treatment plant at Gaza. Wastewater treatment plant at Gaza and its infiltration basins are considered the primary sources of pollution for the ground water and sea water. The historical records of Gaza Wastewater Treatment Plant from January 2000 to October 2004 were collected and evaluated to assess the system performance in term of removal efficiency for the BioFilter-Aerated Lagoon combined system. This study attempts to highlight the factors leading to the inadequate performance of GWWTP in removing organic matter, solids, nutrients and microorganisms. The efficiency of the different stages of the treatment process and the overall plant performance has been demonstrated.Collection and analysis of available historical data revealed a constantly decreasing removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) and fecal coli form (FC). Analysis of data showed that the combined system removal reached 91%,87%,88%,97.5% and 21.5% of the influent BOD5,COD,TSS,FC and TKN respectively with an effluent concentration of 35.2 mg/l,110 mg/l,53 mg/l,7.73E+6 and 69.2 mg/l. The decrease in the removal efficiency of the pollutants appeared to be due to the increase in the hydraulic and organic load that exceeded treatment plant designed capacity, inaccurate design parameters and inadequate operation.Over hydraulic and organic loading, increasing values of TSS than normal values, inadequate design of the plant and inadequate plant management are the main factors behind the drop in the treatment system performance. The study presents proposals like the construction of another anaerobic lagoon and a grit chamber and splitting the flow equally between the trickling filters and the aeration lagoon along with the construction of another final settling tank which can be introduced as short, simple and economic solutions to overcome and improve the inefficient and poor treatment plant performance.
CHAPTER ONE
INTRODUCTION
1.1Background of the study
The sites for disposal of wastewater have traditionally been natural watercourses, land and the coastal waters. One of the major sources of organic pollution is effluents from sewage treatment works. Prevention of pollution of natural resources such as land and water by the waste water and adequate preparation or renovation of the wastewater before reuse, are further important considerations in formulating and designing appropriate waste water disposal arrangements.
Given the characteristics of raw wastewater and the requirements of disposal or reuse, the waste water usually requires some type of preparation or treatment before it is rendered fit for disposal or reuse. Generally, in many situations involving domestic wastewater, the treatment consists of removal of suspended solids and 5-day, 20°C BOD, which are the two usual parameters of prime interest. The degree of treatment provided to the wastewater will largely be based on the effluent standards prescribed by the regulatory agencies when the treated effluent is to be discharged into a watercourse or land. If the effluent is to be reused, the quality of the effluent required to support such reuse will indicate the degree of treatment necessary. The complete treatment of wastewater is brought by a sequential combination of various physical unit operations, and chemical and biological unit processes. The general yardstick of evaluating the performance of sewage treatment plant is the degree of reduction of BOD, and suspended solids, which constitute organic pollution. The performance efficiency of treatment plant depends not only on proper design and construction but also on good operation and maintenance.
Performance evaluation of existing treatment plant is required (1) to assess the existing effluent quality and/or to meet higher treatment requirements and, (2) to know about the treatment plant whether it is possible to handle higher hydraulic and organic loadings. Performance appraisal practice of existing treatment plant units is effective in generation of additional data which also can be used in the improvement in the design procedures to be followed for design of these units. Existing facilities can be made to handle higher hydraulic and organic loads by process modifications, where as meeting higher treatment requirements usually requires significant expansion and/or modification of existing facilities.
One of the primary considerations in evaluating an existing wastewater plant is in the area of plant operation and control. A major tool required for proper process control is frequent and accurate sampling and laboratory analysis. Poor conditions of sewerage system, improper design of the plant and organizational problems are important factors that cause treatment plant not to meet the effluent standards. Overloading due o increase in population and water use, discharge of trade effluents are other reasons of recent times for the poor performance of waste water treatment plants. The treatment efficiency may be badly affected if the system is hydraulically under loaded.
Gaza Strip (GS) has a coastline of 40 km at the eastern extreme of the Mediterranean and on the edge of the Sinai Desert. GS has a total area of 365 square kilometers (MOPIC, 1998) and the population is estimated to be around 1,500,000 people.
There are more than 7000 wells (PWA, 2004) existing in Gaza strip most of which is privately owned and used for agricultural purposes. In most regions, over pumping has resulted in extractions greatly exceeding replenishment which in turn has caused the saltwater interface to move inland (CAMP,2001). Continuing over pumping for agricultural and domestic use will deplete the fresh water aquifer resulting in its replacement with sea water. The extractions for agricultural purposes now exceed 80 million cubic meters (MCM) per year, while rainfall replenishment is only about 40-50 Mcm per year ( Al-Jamal, K and Yaqubi, 2003) Agricultural return flows are about 20 MCM and often carry pesticides and nitrates, a major pollutant in the upper levels of the aquifer (CAMP, 2001). Also, sea water intrusion has caused the closing of many wells (CAMP, 2001)
Surface water in Gaza strip consists mainly of wadi Gaza, which originates in the Negev Desert, is the major one. Its catchments area is about 3500 km2 (CAMP, 2001). The estimated average annual flow of Wadi Gaza is 20 to 30 MCM (PWA, 1997). When surface runoff occurs, it occurs during a limited number of days. Presently, surface water resources are not anymore available in the Gaza Strip due to Israeli violations.
