The current study presents a detailed evaluation and comparison between two integrated anaerobic–aerobic systems for biological wastewater treatment under equal conditions in all aspects (wastewater characteristics, climatic conditions, reactor sizing, and even the measurement methods). The two examined systems are (i) a hybrid upflow anaerobic sludge blanket (hybrid UASB) coupled with integrated fixed-film activated sludge (IFAS) and (ii) a conventional UASB coupled with activated sludge (AS). The present comparative study aims to evaluate and assess the effect of adding carrier-filling media on the performance of the classical integrated UASB-AS. The two parallel pilot-scale systems, hybrid UASB-IFAS and UASB-AS, were installed and operated at a wastewater treatment plant. Three sets of experiments were conducted to examine the influence of the hydraulic retention time (HRT) on the consequent organic and hydraulic loads, temperature, and recirculation rate of the proposed systems. The main results showed that the two investigated systems had a comparably high efficiency for the removal of organic matters and ammonia. Moreover, a paired sample t-test indicated there was a statistically significant effect of the filling media, and the performance of the hybrid UASB-IFAS increased significantly compared with that of the UASB-AS system. An additional benefit of the filling media on the hybrid system was its high stability when changing the organic and hydraulic loads. The optimum HRT was 6 h, with a total chemical oxygen demand (TCOD) percentage removal of approximately 95% in both examined systems. Treatment of sewage under high and low temperatures indicated that increasing the temperature improved the efficiency of the overall process for both systems significantly.
a b s t r a c tSewage sludge conditioning with chemicals has been employed widely to improve thickening and dewatering processes. Although it is a good alternative for process improvement, its cost is high. It is important to find effective and cheap conditioners. Large quantities of cement kiln dust (CKD), which proved to be a good chemical stabilizer of sewage sludge, are emitted from cement factories. In this study, the effect of using CKD on the thickening and dewatering performance of sewage sludge were investigated by zone settling test, free gravity drainage test, specific resistance to filtration (SRF) and natural drying tests. The results indicated that adding CKD to sewage sludge by 60% of total solid could improve the sludge thickening, dewatering as well as stabilization. The settleability of sludge was improved as follows: the zone settling velocity increased from 43. m/kg) and the actual dewatering time required to achieve sludge with solid content more than 20% reduced from 5 to 2 d, while the pH value remained in the required range for stabilization.
The objective of anaerobic digester start-up is to achieve steady-state operation and the required reduction performance in the shortest possible time. The present study aims to assess a novel strategy to start-up pilot scale mesophilic anaerobic digester with internal inoculums; the operational parameters such as feed concentration and operating temperature were also evaluated. Three pilot scale anaerobic digester systems were designed and manufactured. They were equipped with all necessary instruments for measurements, operation and control. Each system consists of a feed tank, a reactor (anaerobic digester), a gas storage tank, and a displaced water collecting tank. The digester start-up was achieved successfully and smoothly without any operational problems. The feed concentration had minor effects on the performance of the digester start-up while the operating temperature has approximately no effect.
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