Issues regarding the discharge of waste liquid and residue from ammonia-alkali ammonia stripping

This is a news report: High-tech innovations have turned waste residues and liquids from the Nanhua Alkali Plant into valuable resources. Recently, an inspection team from Jiangsu Province, tasked with “creating an environmentally model city,” evaluated the environmental management efforts at the Lianyungang Alkali Plant operated by Nanjing Chemical Industry Co., Ltd. After conducting on-site inspections of the hardware and software facilities for environmental protection at the Lianyungang Alkali Plant, the leaders and experts from the inspection team spoke highly of the plant’s achievements in recent years. Specifically, they commended its successful application of advanced technologies to treat waste residues and liquids, thereby accelerating its transition toward a circular economy. As a **large-scale key chemical enterprise**, Lianyungang Alkali Plant produces 1 million tons of soda ash annually; it is one of the three major soda ash producers in China. Due to the specific nature of the ammonia-soda process, for every ton of soda ash produced, 10 cubic meters of waste liquid is discharged, along with waste residue containing 3%–5% calcium as its main component. In the early days of its operation, the plant relied on the traditional method of building dams to collect and clarify waste liquids before discharging them into the sea. Every year, tens of millions of yuan are invested in the expansion and renovation of the slag disposal site. With the continuous expansion of production scale, the slag yard designed for an annual output of 600,000 tons can no longer meet the discharge requirements of chemical production. Currently, regarding the treatment methods for ammonia-soda waste liquid and residues, domestic and foreign soda ash enterprises primarily employ the traditional approach of constructing dams to retain the residues; the waste liquid is then clarified before being discharged ； Second, it is concentrated and then discharged into the deep sea via ships ； Third, an advanced solid-liquid separation method is employed: after pressure filtration, the treated liquid that meets standards is discharged directly, while the solid residue is stacked for reuse. How to effectively handle the waste residues and liquids generated in soda ash production has always been a challenge that affects the survival and development of ammonia-soda ash plants around the world. Starting in 2000, with a view to the long-term interests of its development, Lianyungang Alkali Plant put forward the strategic concept of “building an environmentally friendly and high-tech platform for Lianyungang Alkali Plant”. Regarding how to utilize new high-tech platforms for comprehensive environmental management, the plant organized its engineering and technical personnel to collaborate with relevant domestic entities. By employing high-tech methods, they gradually developed new techniques for treating waste liquids. At the same time, it has set its sights on the world’s most advanced filter press engineering technologies today. By employing new processes, technologies, and methods to treat waste liquids, Lianyungang Alkali Plant has accelerated its transition toward a circular economy. In 2003, the plant cooperated with Finland’s LAROX company for the first time. After numerous field-scale pilot tests, it applied a new filtration technology to the treatment of alkali residue for the first time. In September 2003, the factory invested over 40 million yuan to purchase two Finnish PF filter presses, thus establishing China’s first waste hydraulic filtration facility. By first concentrating the production wastewater in a clarifier, and then feeding the thick slurry into a filter press for solid-liquid separation, it has been possible to successfully apply the currently advanced filter press engineering technology in environmental treatment. Since its commissioning two years ago, the filter press system has processed a total of approximately 6 million cubic meters of wastewater. The volume of alkali sludge after filtration is only half that of the original sludge, with a moisture content of less than 50%. This not only effectively extends the service life of conventional sludge disposal sites and significantly reduces the required storage space, but also helps conserve valuable land resources locally ； Meanwhile, the waste residue cake generated by the filter press can be used as backfill for construction sites or as an auxiliary material in the construction of high-grade roads. On this basis, the plant has continuously tackled challenges, actively exploring new pathways for a circular economy in the treatment of waste liquids for soda ash enterprises. This year, another 60 million yuan was invested to add three filter presses. Additionally, renovations were carried out to recycle wastewater from the slag yard; utilizing the waste liquid that had been concentrated through clarification tanks, a new project for recycling wastewater from the coal ash slag yard was established. After the wastewater recycling project at the slag yard became operational in November this year, it not only resolved the environmental issue of desulfurization and dust removal from the flue gas of the plant’s power station boilers, but also helped the enterprise save 2.4 million tons of water annually and increase its profits by 810,000 yuan. Meanwhile, Lianyungang Alkali Plant also expanded its existing calcium chloride production facility from 20,000 tons per year to 40,000 tons per year. It makes full use of the clarified supernatant obtained after pressure filtration, which is then transported to salt pans for further evaporation and precipitation into brine; calcium chloride with good economic value is directly extracted from this brine. While turning waste into valuable resources, it achieves a win-win situation for both environmental benefits and corporate economic efficiency. I totally agree with their approach, but I cannot approve of investing 40 million and then another 60 million to purchase filter presses. When introducing technology, we can’t rely solely on importing equipment to get by.