Tailwater recycling saves cost, boosts production of aquaculture

SHIJIAZHUANG, Jan. 30 (Xinhua) -- Tailwater is not wastewater, as is found out by a major aquaculture city in China's northern province of Hebei.

"Since the middle of January, we harvested up to 2,500 kilograms of prawns every day. Recycled water played an important role," said Yin Xiangguang, head of a mariculture farm in Laoting County of Tangshan. Tangshan has been promoting green mariculture.

At the entrance to his aquaculture farm, a water wheel-like roller spins without stopping. The tailwater flows into the roller and microfilter. Large particles of residual bait, fish, and prawn feces are filtered out.

In the following steps, the farm carries out nitrogen removal treatment and ultraviolet disinfection. The treated water is heated and returned to the prawn ponds for reuse, while a small amount of tailwater is discharged into the sea after special treatment.

Yin's mariculture farm raises more than 10 varieties of aquatic products, including prawns and flounders.

In 2020, the farm built a water recycling plant, which increased the recycling rate of aquaculture water to higher than 80 percent.

The mariculture farm has reaped huge benefits from investment in water recycling facilities. "In the past, we pumped in water from the sea," said Yin. "This caused stress reactions of prawns and some loss."

With the use of recycled water, the temperature and quality of the water remain constant, ensuring a stable living environment for fish and prawns. Nowadays, the mariculture farm only needs to be supplied with a small amount of seawater.

Tangshan City has a coastline of over 250 kilometers and more than 930,000 mu (about 62,000 hectares) of area used for seawater aquaculture. Local output of aquaculture totals 247,000 tonnes.

The city aims to speed up the green and low-carbon transformation of the aquaculture industry.

The Tangshan Caofeidian Huitong Aquatic Science and Technology has set up tens of sedimentation tanks outside its aquaculture farm for treating tailwater.

The five-stage sedimentation tanks purify the tailwater for further use, said Tian Zhongxi, office director of the company.

Many aquaculture farmers have already experienced the benefits of eco-farming, said Su Wenqing, an official in charge of aquatic technology promotion in Tangshan City.