With the rapid development of intensive mariculture, lots of mariculture wastewaters containing residual feed and excrements are discharged into marinelands, leading to coastal pollution. Recently, the environmental problems caused by the discharge of mariculture wastewater have been paid much attention, as have other breeding industries in China. In fact, organic solid waste accounts for most of the pollutants and can be reduced by precipitation or filtration technologies, after which the supernatant can be easily treated by ecological methods. Some national guidelines and relevant local standards have been issued to strictly control the mariculture wastewater, but there are still few effective technologies for mariculture wastewater treatment due to its high salinity and extremely low pollutant concentration. This paper aims to propose feasible pollution control methods of mariculture wastewater according to the wastewater characteristics from different mariculture modes. For raw ammonia-based wastewater, it should be sequentially treated by precipitation, nitrification and denitrification and ecological methods, which would target solid waste, organic carbon/nitrogen and phosphorus removal, respectively. For the nitrate-based wastewater, this just needs denitrification filters and ecological methods for nitrate and phosphorus removal. After an overview of pollution control strategies for different types and scales of industrial mariculture wastewater treatment, some challenges are also mentioned.

This review critically evaluates the algal–bacterial consortium (ABC) as a promising technology for wastewater treatment, carbon capture and storage, while also assessing its challenges and opportunities. The ABC system, characterized by the coupling of algae and bacteria, not only removes pollutants and reclaims resources but also helps in reducing greenhouse gas emissions. This system harnesses algal photosynthesis and bacterial degradation of organic matters to establish a carbon cycle, enhancing biomass production and pollutant removal. Despite its promise, the ABC process is subject to several hurdles, including sensitivity to low temperatures, reliance on artificial illumination, and the potential for algal biomass contamination by toxic substances. To capitalize on its full potential, continued research and technological advancements are imperative. Future investigations should focus on optimizing the system’s operational efficiency, developing precise process models, exploring avenues for resource recovery, and broadening the scope of its applications. By surmounting these challenges, the ABC system has the capacity to make a significant impact on sustainable wastewater management and carbon fixation.

The sediment microbial community plays a key role in the cycling of organic matter in marine ecosystems. The characteristics of the sediment microbial community are significantly related to changes in the environment. In this study, we analyzed the diversity and distribution of microbial communities in sediments from different geographical regions (the Liao River estuary, Yellow River estuary, hypoxic zone, and offshore zone) of the Bohai Sea using high-throughput sequencing. The results showed that the community richness and diversity (especially the unique diversity) of the Liao River estuary were larger than those of the Yellow River estuary, hypoxic zone, and offshore zone. The phylum Proteobacteria dominated in the Liao River estuary (46.26%), hypoxic zone (76.19%), and offshore zone (69.79%), while the dominant phylum in the Yellow River estuary was the Bacteroidetes phylum. The genus Gillisia was the dominant genus in both the Liao River estuary and Yellow River estuary. The offshore zone and hypoxic zone shared the same dominant Photobacterium genus. The results of Pearson correlation and redundancy analysis showed that environmental parameters such as nitrite, silicate, nitrate, phosphate, ammonia, dissolved oxygen, pH, and salinity interfered significantly with the structure and diversity of the microbial community. The results of this study will provide support for future research on the interaction mechanism of pollutants and microorganisms in the estuaries and a typical hypoxic zone of the Bohai Sea.

In this study, magnetic CuFe₂O₄, MgFe₂O₄, and ZnFe₂O₄ nanosphere photocatalysts were prepared by the sol–gel method at 300 °C, 400 °C, and 500 °C, respectively (named as CF300, CF400, CF500, MF300, MF400, MF500, ZF300, ZF400, and ZF500). The characterization by X-ray diffraction (XRD) revealed that the optimal calcination temperature was 400 °C. Then, CF400, MF400, and ZF400 were used to treat high-concentration ammonia nitrogen wastewater (HCAW, 1000 mg/L) at different pH levels. The result showed that the optimal pH for CF400, MF400 and ZF400 to degrade HCAW was 9.0, and CF400 required a shorter illumination time (80 min) than MF400 and ZF400 (120 min) to completely remove ammonia nitrogen from HCAW. However, CF400 was unstable and decomposed, and a blue substance was observed during the magnetic recovery experiment. The recovery rate of ZF400 (66.7%) was higher than MF400 (53.2%) with no decomposition phenomenon, and the ammonia nitrogen removal rate of ZF400 remained above 90% after five cycles. Additionally, the ammonia nitrogen removal rate of ZF400 could reach 80.2% when the ammonia nitrogen concentration was as high as 5000 mg/L. Therefore, compared with CF400 and MF400, ZF400 was more suitable for treating HCAW.

Due to stricter municipal wastewater discharge standards, there is an increased need for further treatment of nitrate in the secondary effluent of wastewater treatment plants. This is achieved through denitrification by the addition of external carbon sources, which leads to increased costs in wastewater treatment. The aim of this study was to examine the possibility of simultaneous removal of nitrate and phosphorus from simulated secondary effluent by employing a sponge-iron-based denitrifying filter at room temperature. The results indicate that at hydraulic retention times of over 2 h, more than 60% of the nitrate was reduced to ammonia and nitrite via iron-based abiotic nitrate reduction. However, sponge iron easily scaled after two months of operation. Therefore, a little glucose was added to the influent, resulting in a final COD/N ratio of 1:1. Mixotrophic nitrate reduction was observed, and the rust of sponge iron was successfully dissolved. Batch test results demonstrate that biological nitrate denitrification accounted for 70.0% of the total nitrate reduction. Additionally, high-efficiency phosphorus removal through the chemical reaction of released iron and phosphorus was achieved throughout the entire experiment, with removal efficiencies of more than 90% at hydraulic retention times of over 2 h. Moreover, high-throughput sequencing data show that the species diversity obviously increased after adding organic carbon, suggesting the coexistence of heterotrophic and autotrophic denitrifiers. Hence, the sponge-iron denitrifying filter has considerable prospects in the field of secondary effluent treatment and is likely to be the future direction of zero-valent iron application in sewage treatment.