Chemical fractionation and risk assessment of trace elements in sewage sludge generated from various states of Pakistan.

In the developing world, rapid urbanization and industrialization produces an enormous volume of wastes daily. This study was aimed to explore the potential and risks associated with sewage sludge through the characterization and fractionation technique. Sewage sludge samples were collected from various wastewater treatment in five different cities of Pakistan. Considerable amounts of macro-elements were detected in all types of sewage sludge samples. The pHw of all sewage sludge were neutral to slightly alkaline in reaction. Total organic carbon (TOC) was maximum (18.73%) with Coca-Cola sewage sludge (CSS) while the minimum (14.69%) was with Water and Sanitation Agency (WASA) sewage sludge (WSS). Percent relative distribution of cadmium (Cd) was higher in residual fraction (F4) up to 52% in the Nestle wastewater treatment plant, Sheikhupura (NSS). The chromium (Cr) concentration in Kasur sewage sludge (KSS) was extremely in mobile fraction (exchangeable) as compared with all other sludge samples, therefore showing a higher level of risk assessment code. While in the case of Iron (Fe), mobility was less and its maximum portion was noted in residual fraction (F4) of all sewage sludge samples. Percent distribution of manganese (Mn) showed variable trends for different sewage sludge samples. Zinc (Zn) concentration showed high mobility (exchangeable fraction) in case of NUST wastewater treatment plant, Islamabad (NTS) (31.16%) and WSS (37.83%) as compared with other sewage sludges. The risk assessment code indicated that Zn and Ni had a medium level of risk with I-9 Sector wastewater treatment plant, Islamabad (ISS), CSS, KSS, and NSS whereas these pose a high risk with NTS and WSS. Based on physicochemical properties, nutrients, trace elements, mobility, and risk assessment code, it was concluded that KSS should not be recommended at any application rate while NTS and WSS may be used at low application rates whereas ISS, CSS, and NSS may be used for agricultural crop production.

Response of rice advance line PB-95 to potassium application in saline-sodic soil.

A field experiment was conducted to evaluate the response of rice crop to potassium fertilization in saline-sodic soil during 2005. Soil samples were collected before transplanting of rice crop and analysed for physical and chemical properties of the soil. In this experiment five rates of K2O (0, 25, 50, 75 and 100 kg ha(-1)) were applied in the presence of basal doses of N and P2O5 i.e., 110 and 90 kg ha(-1), respectively. Whole of P, K and 1/2 of N were applied at the time of rice transplanting. Twelve and halfkg ha(-1) ZnSO4 was also applied 15 days after rice transplanting. The remaining half of N was applied 30 days after rice transplanting. The system of layout was Randomized Complete Block Design with four replications. The net plot size was 6x4 m. Fertilizer sources of NPK were urea, TSP and SOP, respectively. Rice salt tolerant line PB-95 was used as test crops. The data of growth parameters and yield was recorded and samples of paddy and straw were collected treatment-wise and analysed for N, P and K contents. Soil samples after harvesting the crop were also collected, processed and analysed for the changes in the extractable soil K. The results showed that increasing rates of potassium fertilizer increased the number of tillers m(-2), plant height (cm), 1000-paddy weight and paddy as well as straw yield significantly. Maximum paddy (3.24 t ha(-1)) and straw (3.92 t ha(-1)) yields were obtained in T5 (100 kg K2O ha(-1)) which was at par with T4 (75 kg K2O ha(-1)). With increasing rates of potassium fertilizer, concentration of potassium in paddy and straw increased significantly. After harvesting the crop, the extractable potassium contents of soil increased from that of the original soil. It was concluded from the results that there was an increase of 30.65% in paddy over control by applying potassium (100 kg K2O ha(-1)) in saline-sodic soil.