No abstract

With the booming construction of sewage treatment plants aiming at environmental protection, China has to face an emerging urgent task to address the sludge treatment and disposal problem. However there is a big controversy in China about the sludge treatment and disposal strategies. Some scientists suggest incinerating, while others insist on landfilling. In this paper, from the perspective of sustainable development and cyclic economy, a detailed analysis of nutrients cycle mainly related to nitrogen and phosphate before and after industrialization was made and a view that sludge should go back to soils to re-establish a sound nutrients cycle was put forward. Then the feasibility for sludge recycle to soils was discussed and some land application methods for sludge were introduced. At last, a successful case of producing compounded fertilizer from dewatered sludge in Northeast China was described in detail.

The effects of molybdenum (Ⅵ) on the denitrification efficiency of activated sludge process were investigated with batch tests. The results indicated that up to 5 mg/L of Molybdenum (Ⅵ) concentrations in the liquor of activated sludge process could accelerate the nitrate removal rate, exhibiting maximum stimulation at 1 mg/L. Up to 4 mg/L of Molybdenum (Ⅵ) concentrations, the COD removal efficiency was enhanced. Up to 1mg/L of Molybdenum (Ⅵ) concentrations, the TTC-DHA was enhanced but higher concentration showed inhibitory effects. Based on the integrated effects of Molybdenum (Ⅵ) on nitrate and COD removal with the TTC-DHA change, 1mg/L of Molybdenum (Ⅵ) is proposed as the best concentration for denitrification of activated sludge.

Struvite precipitation in sludge dewatering filtrate was achieved in a lab-scale sequencing batch reactor. The influence of the operational conditions on the struvite precipitation process has been studied. These operational conditions include stirring rate of the reactor, reaction time and sedimentation time. Experiments indicated that stirring rate of the reactor within 50 rpm to 250 rpm had no strong influence on the formation of struvite. As reaction time increased, there was a slight positive effect on the removal of Mg2+, NH4+ and PO43-. Suggested reaction time is 40-80 minutes based on our experiments. In order to obtain the lower turbidity and the lower PO43- concentration in the decanting filtrate of the batch reactor, the minimum sedimentation time should be more than 30 minutes.