Utilization of calcium lactate filter cake as a promising water quality improver in Eriocheir sinensis ponds with high pH

In summer, the pH of the water in aquaculture ponds often becomes excessively high, which can lead to negative effects on Eriocheir sinensis . Calcium lactate filter cake (CLFC) is a by-product in lactic acid production, which contains organic acid and calcium salts. But it’s not been utilized effectively, leading to resource waste. This study aimed to evaluate the effects of CLFC use in E. sinensis ponds with high pH on water quality (physical and chemical parameters and microbial community), growth performance and calcium content of crab. The physical and chemical parameters showed a significant reduction in the pH levels of pond water and sediment ( P < 0.05), while calcium ion concentration and oxidation-reduction potential (ORP) of water were remarkably increased ( P < 0.05) after the use of CLFC. The aquatic microbial community analysis showed that Sobs index of community richness exhibited a significant increase in the CLFC group ( P < 0.05). The physical and chemical parameters and aquatic microbial community correlation analysis revealed that the pH, ORP and calcium ion concentration of water were significantly correlated with the microbial community ( P < 0.05). Growth performance of crab showed that the final body weight, weight gain rate, and specific growth rate in females significantly increased compared with the control group ( P < 0.05). The gonadosomatic index and condition factor in males was significantly higher in the CLFC group ( P < 0.05). In summary, CLFC can serve as a water quality improver, reduce pH and supplement calcium, thus promoting the growth of crab. This study demonstrates the utilization value of CLFC in the aquaculture industry, provides a practical solution for pH regulation in crab aquaculture, and explores a sustainable way to valorize industrial by-products. • Calcium lactate filter cake can solve the problem of excessively high pH levels in pond water, as a water quality improver. • Calcium lactate filter cake reduces pH, while increasing calcium ion concentration and oxidation-reduction potential of water. • Calcium lactate filter cake promotes the growth performance of crab through improving water quality and providing calcium sources.