THE PROJECT – Cold Weather Nitrification
Ninjan, a city situated in the Northern Province of China has a population of 440,000 inhabitants. The city has severe winter weather conditions during their winter season. To reduce water pollution, the authorities had already planned construction of a 10,000 m3/day sewage wastewater treatment plant to manage the city’s wastewater. Originally the plant had been designed involving the use of an oxidation ditch pond variant for an activated sludge process to meet only the statutory BOD removal in order to achieve the statutory compliance.
THE PROBLEM
However, due to changes in legislation, the plant was required to meet Chinese class 1 compliance criteria for BOD, TSS, TN < 15 ppm, Ammonia < 5 ppm and COD, 50 ppm. Due to extreme cold weather conditions, achieving COD < 50 ppm and Ammonia < 5 ppm posed to be a significant challenge.
A decrease in liquid temperatures during the winter months reduces the biological activity and thus the removal rates of the activated sludge process. This reduction in the biological activity and removal kinetics would require the volume of the existing aeration tanks to double in order to compensate for the new statutory compliance.
THE CHALLENGE: Cold Weather Nitrification of Municipal Wastewater
Due to the inherent problems related to the cold winter conditions and space restrictions, the city was looking for a solution which could deliver the required results within the constraints of the ongoing full utilization and the plant being under construction.
Principle challenges associated with the project were:
- Very low liquid temperature (8-10 Degree C) during winter period resulting in lower biological activity of the activated sludge
- Severe constraints as the plant was currently under construction and utilizing existing infrastructure with a lack of further space availability
- Inlet load fluctuated greatly between spring and winter seasons due to specific water usage patterns which required treatment to new stringent standards of BOD, TSS, TN < 15 ppm , Ammonia < 5 ppm and COD < 50 ppm under all conditions.
THE SOLUTION: LEVAPOR-IFAS Upgrading of existing Activated Sludge Plant
Due to our experience with cold weather nitrification for municipal sewage wastewater, a hybrid activated sludge based IFAS process using Levapor MBBR /IFAS media was suggested for the proposed modification of the plant.
After extensive trials were conducted on site under different scenarios of inlet wastewater conditions consisting of; temperature, BOD, COD, TSS and TKN, a design was implemented on site taking into consideration the existing aeration tanks currently under construction.
During the trials, it was found that even at a shorter HRT of 3.5-3.8 hours, the required results can be achieved for the plant and also inlet wastewater treatment capacity can be also doubled to 20-22,000 m3/day if required. Already the client was planning to construct another 10,000 m3/day plant for meeting full treatment requirement, it was decided to double the capacity also.
Based on the pilot trials and previous experience, the following design was proposed.