By Jiao Fenghua, Wang Zhencai
Ningbo, a coastal city in east China’s Zhejiang Province, has taken great strides towards building the city into “a global marine city.” In recent years, the rise of the marine economy has helped the marine aquaculture industry become an important growth pole for the economic development of the city. In the meantime, however, the problem of tail water treatment has arisen, challenging the growth of the industry.
To tackle the problem effectively, Ningbo has focused on the comprehensive management of key sea areas to improve the ecological environment for marine aquaculture. Taking into consideration its two major development goals of being both “green” and “rich,” the city has constantly innovated and explored new models of aquaculture tail water management with industrial upgrading as the core and scientific governance as the guidance, in order to build a new modern aquaculture ecology. At present, the city’s large-scale aquaculture farms with a water surface area of over 30 mu (2 hectares) have basically discharged their tail water after treatment. According to relevant regulations, the farms have also set up a long-term management system, carried out the monitoring of aquaculture tail water, and comprehensively promoted the mode of eco-friendly aquaculture.
To improve the yield of South American white shrimp for more economic benefits, the town’s aquaculture park has actively promoted the mode of high-elevation pond intensive breeding, achieving the transition from the mode of traditional extensive breeding to modern eco-friendly intensive breeding. At present, the park’s annual yield of South American white shrimp per mu (1/15 of a hectare) has reached 2,500 kilograms. The economic benefit of this mode is 8-10 folds the benefit of the traditional mode.
The South American white shrimp eco-friendly tail water treatment mode removes from the tail water 82.71 percent of inorganic nitrogen, 65.09 percent of labile phosphorus and 52.88 percent of chemical oxygen demand, achieving the win-win of economic and environmental benefits.
So far, the city’s Ninghai County has built 75 sea water aquarium tail water treatment demonstration sites, and established 44 healthy demonstration aquariums at or above the provincial level. The multi-level treatment has turned tail water from waste into treasure, meeting the primary requirements of the “Regulation on Marine Aquaculture Water Discharge” (SC/T 9103-2007, a national industry regulation since 2007).
With regard to top-level design, the city’s Fenghua District has worked out a program (2018-2022) and an action plan (2021) for aquaculture tail water treatment in the district, with policies tailored for each farm according to realities on the ground. With regard to classified treatment, the district has taken targeted measures, taking into consideration the environment, category, water quality, and other factors of the different types of aquariums, such as sea water ponds, intensive breeding ponds, and fresh water ponds.
Today, the coast of Ningbo is dotted with upgraded modern green aquaculture bases, which together form an ecological barrier between the internal and external river systems protecting the local water environment. Ningbo’s advanced experience in aquaculture tail water treatment provides new ideas and new inspirations for the development of eco-friendly marine aquaculture.