Quick start-up of Mudanjiang wastewater treatment plant and factors influencing phosphorous removal

Successful start-up of a full-scale wastewater treatment plant (WWTP) is a key issue for the
succeeding operation of WWTP on the one hand and the nutritious phosphorus removal is of
great concern on the other. After the construction of Mudanjiang WWTP with a flow rate of
100,000 m3 d-1 in Heilongjiang Province of China, a novel way of start-up through feeding
wastewater continuously into the system was attempted against the conventional start-up
method of inoculating activated sludge in the aeration tank by feeding wastewater
intermittently. Activated sludge was cultivated and proliferated in the aeration tanks instead of
dosing acclimated sludge from other source. After one-month’s start-up operation, MLSS, SV
and SVI increased to 2.5 kg m-3, 30% and nearly 80% respectively, which indicated that quick
and simple start-up had been achieved. After successful start-up, an investigation into
phosphorus removal was conducted with the emphasis on influencing factors such as ORP
and NOx-N concentration etc. When the aeration tank was switched from aerobic to anaerobic
mode, phosphorus removal efficiency of 80% could be realized within the whole treatment
system. Experimental results revealed that an ORP of -140 mV and NOX-N of 2 mg l-1 were
critical for the anaerobic phosphorus release, and DO in the range of 1.7-2.5 mg l-1, BOD5/TP
of 20-30 and SVI of 70~80 as well as SRT of 5 days were the optimal phosphorus removal
conditions for the aeration tanks.