Vacuum-assisted thermal drying of wastewater treatment sludge.

Sludge drying is one of the main problems of wastewater treatment plants. It is very important to facilitate the drying process in terms of drying efficiency, time duration, and cost of the processes, so that transportation and dumping of sludge will accordingly be realized effectively. In this study, vacuum assisted thermal drying was studied. Under vacuum conditions, the water content of the sludge was examined easier than at atmospheric pressure in the drying process. For this reason, in this study, time, temperature, and sludge mass surface area on drying efficiency were evaluated under two different pressure levels, such as 30 mbar and 1,000 mbar. To optimize these parameters, the Response Surface Methodology approach was utilized. Results showed that the effect of vacuum condition on sludge drying was remarkable at obtaining at least 65% of solid material ratio in sludge, which is the lowest limit value on landfilling legislation in Turkey. Data obtained from the study shows that, especially at high temperatures, contribution on sludge drying of vacuum condition is more effective in terms of drying time. A smaller sludge surface area is also found more significant on vacuum drying.Implications: Drying the sludge under low pressure shortens the drying time. It is possible to reach higher solid material ratio under low pressure. Time, temperature, and surface areas of sludge are effective parameters in vacuum drying.

Optimization of treatment leachates from young, middle-aged and elderly landfills with bipolar membrane electrodialysis.

In this study, a bipolar membrane electrodialysis (BMED) process, which is thought to be an effective treatment method for leachate, was evaluated for leachates of three different ages ('young', 'middle-aged' and 'elderly'). The leachates were pretreated to eliminate membrane fouling problems prior to the BMED process. Experimental studies were carried out to determine optimal operating conditions for the three differently aged leachates in the BMED process. According to the experiment results, there was a high removal efficiency of conductivity determined at 4 membrane - 25 V for young and elderly leachate and at 1 membrane - 25 V for middle-aged leachate. It was found that the operating times required to reach the optimal endpoints (at conductivity of about 2 mS/cm) of BMED process were 90, 180 and 300 min for the middle-aged, young and elderly leachates, respectively. Under the optimum operating conditions for the BMED process, removal efficiencies of conductivity and chemical oxygen demand were determined to be 89.5% and 60% for young, 82.5% and 30% for middle-aged and 91.8% and 26% for elderly leachate, respectively.