Background and purpose: Currently, there is only one sewage treatment plant in Sercan City in Hamadan province. Extended aeration activated sludge is the main process of the plant and untreated effluent and disposal sludge are used for agricultural activities. The main objective of this research is to evaluate the stabilization degree and reuse potential of disposal sludge from the plant. Materials and methods: This study was undertaken over a 12 months period from March 2001 to March 2002. In this project some indexes of sludge stabilization and reuse including VS/TS ratio, pH, SOUR, floatation, color, odor, coliform and fecal coliform were determined. Results: The annual average ratio of VS/TS and SOUR in disposal sludge from this plant were 0.73 and 3.37 mg02/gr.vs.h, respectively. The average pH was about 7. The disposal sludge was septic and had dark brown color and floated after a short time. Also the annual average of fecal coliform density in disposal sludge was 8.97 ´ 107 MPN/g.ds. Conclusion: The disposal sludge was raw and destabilized. The microbial quality of disposal sludge was lower than the class B of USEPA regulation. Therefore, this sludge can not be discharged to environment or reused.  

Following the increasing growth of population and the reduction of water resources, a huge volume of sludge, which is a subsidiary product of sewage treatment, needs to be disposed safely in order to protect the environment. The aim of the present study is to find an appropriate method for disposal and beneficial application of sludge. Sludge consists of organic materials, nutrients, pathogens, heavy metals, PCBs etc. Regarding the sludge produced from Shahrak Qods Treatment Plant using the proposed management plan, after taking several samplings and physical, chemical and pathogenic tests on the sludge, it was determined that according to the US EP A standards and regulations, the resulting sludge holds the qualities of class B pathogenically. Regarding the heavy metals, it also bears an exceptionally excellent quality, while having large amount of organic materials, nutrients and micronutrients, which represents the fertilizer value of this material. In addition, it was known as the best alternative for land application after testing various alternatives of disposal. For this purpose, Mehrshahr Garden in Karaj was chosen as the most suitable location for using sludge class B. Having carried out certain chemical and physical experiments on the collected samples of soil, the rate of sludge loading based on Nitrogen (as the limiting factor of application), as well as, the area of sludge application were estimated. Meanwhile, a comparative cost evaluation, between the use of chemical fertilizer and sludge application was made, regarding the amount of commercial fertilizer in these lands, which at last resulted into the cost effectiveness of this plan. The preparation of a similar management plan for all treatment plants in the process of design or construction is a necessity, since it is proved that by implementing such a plan, standards and regulations suitable to Iran's condition, could be imposed for disposal or beneficial application of sludge.

In Saudi Arabia, the Riyadh Sewage Treatment Plant (RSTP) uses the activated sludge technology as the secondary treatment process for sewage. Due to the complex nature of the process, a rather simplified, yet practical, steady state model that captures the most important features of the RSTP was developed. Actual operating and design conditions were obtained from RSTP data bank. The monthly average plant data obtained in 1997 was used to calibrate the model by adjusting four parameters: mmax,H, mmax,A, bH and bA (seasonal variation of temperature are therefore embedded within these values) A computer program was developed to solve the resulting model equations. The predictive nature of the proposed model was verified (without further tuning) using five sets of plant data collected in 2003. Model predictions were found to be in excellent agreement with the plant data (within±5%). Simulation results revealed the sensitivity of model predictions to the values parameters.

Sewage sludge treatment has become a primary subject in wastewater treatment and energy production. This paper aims to study the feasibility of power generation by incineration from sewage sludge enriched with impurities like heavy metals. For this purpose, we chose Arak wastewater treatment plant (AWWTP) and used calorific bomb test for examination. The experimental results showed that the heating values of sewage sludge are much less than the predicted records. This relates to the heavy metal and impurities content of sludge. These totally involved 5 to 18% of dried biomass. Therefore, we modified the predicting equation of heating value with respect to both water and impurities content of excess sludge. Finally, regarding the sludge characteristics of AWWTP, an annealing hierarchy programming (AHP) was used to find optimal technologies for dewatering and sludge minimization. Here, 21 criteria are classified in three main categories to rank the technologies regarding their costs, risks and performance. By all these means, a practical solution is introduced for optimal sludge management.

Aerobic biological treatment systems are very suitable for removing contaminants of organic matter in the sewage. Accordingly, the continuity of the inlet flow to the treatment plant, in design and exploitation of these processes, is necessary to consider. One of the differences between industrial and low population areas wastewater, such as military garrisons, and the Municipal sewage, is their volumetric fluctuations. These fluctuations may have a negative effect on the activated sludge process,thus the efficiency of using balancing pool in activated sludge systems has been analyzed in this research. Wastewater treatment process is based on biologically activated sludge method and extensive aeration. In this method, the raw wastewater is directed to the pumping station gravitationally. Results illustrated that, the inlet flow rate to the treatment plant, has high fluctuations from 0 to 40 (m3/hour) at different hours of the day due to the low population. Based on the samplings, it has been determined that the efficiency of activated sludge process in removing the parameters of BOD5, COD, TSS and ammonia during one week is averagely 61, 61, 68 and 24%, respectively. According to the sewage standards, this treated sewage is not suitable for injection into water wells or surface water or for reuse in agriculture. Whilst, using the balancing pond and controlling the inlet flow to the aeration pond at a rate of 12 cubic meters per hour, the removal efficiency of BOD5, COD, TSS and ammonia escalates averagely 90, 90, 89. 19 and 81. 59%, respectively during a week.

Aerobic digestion is commonly used at small plants to stabilize the organic matter in the sludge. The objective of this research was study on the efficiency of the aerobic digester for stabilization of disposal sludge from Serkan city sewage treatment plant.This study was conducted in four stages over seven months from July 2001 to March 2002. Aerobic digestion of sludge was accomplished in the bench scale with 30-liter volume on the environmental health laboratory of Hamadan Medical Sciences University. In each stage, a sample of disposal sludge from sewage treatment plant was analyzed firstly, then a number of sludge samples from bioreactor were considered for 3 weeks. Sludge samples were tested for stabilization and reuse indexes such as: the ratio of volatile solids to total solids (VS/TS), decreasing percent of volatile solids, specific oxygen uptake ratio (SOUR), total and fecal coliform (TC and FC) number. The results showed that the average amounts of VS/TS ratio, SOUR and FC density in disposal sludge of sewage treatment plant were 0.754, 3.395 and 1.93 108 respectively. The amounts of sludge stabilization indexes in bioreactor were 60% for VS/TS ratio after 15 days, 2 mgo2/gr.vs.h for SOUR after 17 days and 40% decrease of VS after 11 days. Also, the average of FC density in bioreactor sludge was 1.08 × 106 after 22 days. These result indicated that the disposal sludge from Serkan sewage treatment plant was raw and destabilized and aerobic digester could stabilized these, after 17 days. In spite of, the maximum level of microbial quality of digested sludge was in class B of USEPA regulation after 22 days. Therefore, the digested sludge may be used for reconditioning the poor soil or forest areas, but never should be used as a fertilizer for the agriculture.