Shandong Huatai Paper Co., Ltd
Shandong Huatai Paper Co., Ltd. is one of the largest pulp & paper companies in China. Due to increased production, the wastewater treatment plant previously supplied by Purac had not capacity to meet the new demands. Therefore, the Huatai Group decided to invest in an anaerobic wastewater pre-treatment plant with a capacity of 60 000 m3/d. Purac was contracted to make the design and supply the equipment for the new plant.
At present, the total COD removal of the ANAMET® plant installed by Purac at Huatai WWTP is among the highest in the world. The plant also has the advantages of strong buffer capacity, stable water quality, low operating cost and high-yield biogas production. The wastewater comes mainly from waste paper pulp production, BCTMP pulp production and concentrated wastewater from straw pulping. Excess sludge from the second stage aerobic wastewater treatment plant also enters into the anaerobic system for digestion. About 50 % of the organic material in the aerobic sludge is digested, decreasing the sludge dewatering and the cost of disposal. This also reduces the operation costs thanks to recycling of N and P. Furthermore, the biogas production is increased which makes it possible to replace coal by biogas as fuel, giving economic and environmental benefi ts.
The equalisation tank serves as a hydrolysis and acidifi cation tank. The organic solids in the wastewater and the recycled excess sludge from the aerobic treatment are converted into soluble organic matter, favouring the anaerobic reaction.
After cooling to approx. 37 oC in cooling towers, the water is pumped by frequency controlled pumps to the ANAMET® anaerobic reactors.
ANAMET® Anaerobic Reactors
The water enters into two completely mixed anaerobic reactors. The soluble organic matter is converted into organic acids, dissociative ammonia and hydrogen sulphide by the presence of acidifying micro-organisms in the bio-sludge. The acids are degraded into biogas, CH4 and CO2. The gas is collected under the dome roofs of the anaerobic tanks. The biogas has a methane concentration of 50 – 60 % and is used as fuel in the nearby power station.
The sludge is separated from the water in a countercurrent lamella clarifier. The settled sludge slides along the plates to the sludge thickening zone under the lamella package. The sludge is collected by a sludge scraper and is recycled to the ANAMET® tanks by means of suction withdrawal pipes and a sludge return pump. The supernatant leaves the clarifi er via overfl ow weirs into the outlet channel and is directed into the aeration system for further treatment.
Flow: 60 000 m3/d
Inlet COD Load: 182 000 kg/d
COD removal: 118 000 kg/d
COD removal rate: 65 – 70 %