Comparative study of smbr and extended aeration activated sludge processes in the treatment of strength wastewaters

One of the complete treatment processes for industrial and municipal wastewater treatment is membrane bioreactor process which has dominant potential in process and operation sections. This study was conducted to compare the performance of extended aeration activated sludge [EAAS] with submerged membrane bioreactor [SMBR] systems in the treatment of strength wastewater, in the same condition. The initial activated sludge was brought from the Plascokar Saipa wastewater plant. The Plexiglas reactor with effective volume of 758 L was separated by a baffle into the aeration and secondary sedimentation parts with effective volumes of 433 L and 325 L, respectively. The chemical oxygen demand [COD] concentration of the influent wastewater of the EAAS and SMBR systems were between 500-2700 and 500-5000 mg/L, respectively. Results showed that the SMBR system produced a much better quality effluent than EAAS system in terms of COD, biochemical oxygen demand [BOD5], total suspended solids [TSS] and ammonium. By increasing the COD concentration, the concentration of mixed liquor suspended solids [MLSS] and the removal efficiency of organic matter in the SMBR system, were increased regularly, however the removal efficiency of COD in the EAAS system was irregular. The average BOD5/COD ratio of effluent in the EAAS and SMBR systems were 0.708 +/- 0.18 and 0.537 +/- 0.106, respectively. These show that the organic matters in the effluent of the SMBR system was less degradable and thereupon more biological treatment was achieved. Nitrification process was completely done in the SMBR system while the EAAS system could not achieve to complete nitrification

Assessment of medical waste management in educational hospitals of Tehran University Medical Sciences

The management of medical waste is of great importance due to its potential environmental hazards and public health risks. In the past, medical waste was often mixed with municipal solid waste and disposed in residential waste landfills or improper treatment facilities in Iran. In recent years, many efforts have been made by environmental regulatory agencies and waste generators to better managing the wastes from healthcare facilities. This study was carried in 12 educational hospitals of Tehran University of Medical Sciences. The goals of this study were to characterize solid wastes generated in healthcare hospitals, to report the current status of medical waste management and to provide a framework for the safe management of these wastes at the considered hospitals. The methodology was descriptive, cross-sectional and consisted of the use of surveys and interviews with the authorities of the healthcare facilities and with personnel involved in the management of the wastes. The results showed that medical wastes generated in hospitals were extremely heterogeneous in composition. 42% of wastes were collected in containers and plastic bags. In 75% of hospitals, the stay-time in storage sites was about 12-24h. 92% of medical wastes of hospitals were collected by covered-trucks. In 46% of hospitals, transferring of medical wastes to temporary stations was done manually. The average of waste generation rates in the hospitals was estimated to be 4.42kg/bed/day

Removal of hexavalent chromium from drinking water by granular ferric hydroxide

Removal of chromium can be accomplished by various methods but none of them is cost-effective in meeting drinking water standards. For this study, granular ferric hydroxide was used as adsorbent for removal of hexavalent chromium. Besides, the effects of changing contact time, pH and concentrations of competitive anions were determined for different amounts of granular ferric hydroxide. It was found that granular ferric hydroxide has a high capacity for adsorption of hexavalent chromium from water at pH 0.968. However, the disadvantage was that the iron concentration in water was increased by the granular ferric hydroxide. Nevertheless, granular ferric hydroxide is a promising adsorbent for chromium removal, even in the presence of other interfering compounds, because granular ferric hydroxide treatment can easily be accomplished and removal of excess iron is a simple practice for conventional water treatment plants. Thus, this method could be regarded as a safe and convenient solution to the problem of chromium-polluted water resources