Optimizing ZLD technology for nitrogen and phosphorus wastewater, and accelerating the ZLD development for industrial wastewater

In recent years, eutrophication of water bodies has become a globally concerning issue. Nitrogen and phosphorus from certain industrial wastewater and domestic sewage are among the primary sources contributing to water body eutrophication. Therefore, reducing the nitrogen and phosphorus emissions in wastewater has thus become an important topic in water body protection. Certain electronic industrial wastewater contain high levels of ammonia nitrogen, necessitating the development of low-investment, low-operating-cost, and highly efficient processes for nitrogen and phosphorus removal to facilitate the comprehensive recycling and reuse of wastewater, thereby reducing potential hazards to drinking water sources and agricultural ecosystems. This approach would enable the electronics industry to progressively transition towards a circular economy development path.

"Zero emission"

The concept of zero emission was first proposed in 1994 by the United Nations University, headquartered in Japan. It refers to activities aimed at continuously reducing the pollutant and energy emissions until they are eliminated entirely. The content involves first controlling and reducing to zero the inevitable liquid, gaseous, and solid emissions produced during manufacturing processes; and secondly, recycling and reusing the energy and resources from those emissions that can be reclaimed, ultimately achieving zero environmental pollution.

Zero Liquid Discharge (ZLD)

Zero Liquid Discharge (ZLD) is a concept that was first introduced by the United States in 1970. The Electric Power Research Institute (EPRI) in the U.S. defines Zero Liquid Discharge as "not discharging any form of water to surface waters (including both direct discharge and seepage), with all water leaving the power plant either as moisture in flue gas or solidified in ash residues." Zero Liquid Discharge (ZLD) refers to the process where industrial water is reused multiple times, and the resulting wastewater with high concentrations of salts and contaminants is almost entirely (over 99%) recovered and recycled, ensuring that no liquid waste is discharged from the facility. The salts and contaminants in the water are concentrated and crystallized into a solid form, which is then either sent to a landfill for disposal or recovered for use as valuable chemical raw materials. The China Water Conservation Technology Policy Outline issued in 2005 explicitly pointed out the development of technologies for the reuse of externally discharged wastewater and "zero emission" technologies. In the standard Industrial Water Usage and Conservation − Terminology (GB/T 21534-2008), Zero Liquid Discharge (ZLD) is defined as achieving no discharge of industrial wastewater from the production water system of an enterprise or organizational unit.

Why is it important to achieve "zero emission"?

On April 16, 2015, the State Council of China issued the Action Plan for Prevention and Control of Water Pollution (hereinafter referred to as the "Ten-point Water Plan"). Based on the requirements of comprehensively controlling pollutant emissions, focusing on conserving and protecting water resources, and fully ensuring the security of the water ecological environment, this plan sets forth more stringent requirements for enterprises regarding water conservation and emission reduction. The plan proposes that by 2020, the quality of the national water environment will have achieved phased improvement, with a significant reduction in severely polluted water bodies; the enforcement of environmental protection laws will be strengthened; more efforts will be made on industrial pollution prevention and control; “ten categories of small” enterprises will be closed down; comprehensive inspections will be conducted on small industrial enterprises with low levels of equipment and inadequate environmental protection facilities. By the end of 2016, in accordance with the requirements of water pollution prevention and control laws and regulations, all production projects that do not comply with national industrial policies and severely pollute the water environment, such as small-scale papermaking, leather tanning, printing and dyeing, dye production, coke making, sulfur refining, arsenic refining, oil refining, electroplating, pesticide manufacturing, etc., had been completely closed down. While enterprises are producing high-quality process water that meets the required standards, how to reuse substantial amounts of wastewater, reduce energy consumption, meet emission standards, minimize environmental pollution as much as possible, and even achieve zero pollution discharge, has become a major challenge for them. Zero liquid discharge of wastewater is the ultimate goal for enterprises to achieve water conservation and emission reduction.

TG Environment − nitrogen and phosphorus wastewater ZLD technology case

Project background: For many years, the water bodies in the Taihu Lake Basin have suffered from severe eutrophication, causing frequent outbreaks of severe blue-green algae blooms. To thoroughly address this severe ecological issue, the local government has implemented stringent measures to maximize control over the total discharge of nitrogen, phosphorus, and other pollutants into Taihu Lake within the surrounding region, and imposed strict requirements for zero discharge of nitrogen and phosphorus on factories in the vicinity.

TG Hylite Environment Technology Co., Ltd. is a national high-tech enterprise that specializes in providing comprehensive water treatment solutions for advanced manufacturing industries such as liquid crystal display, microelectronics, and integrated circuits. In 2016, TG Hylite Environment Technology Co., Ltd. successfully completed a nitrogen and phosphorus wastewater ZLD project at an electronics factory in Kunshan, with a treatment capacity of 16 m3/h. This project requires zero discharge of nitrogen and phosphorus. It employs the AO+MBR biological process, RO desalination and concentration, and MVR evaporation with drying and crystallization.

1. How to truly achieve "zero liquid discharge" for nitrogen and phosphorus wastewater?

TBTG Environment adopted the A/O+MBR biological process for carbon removal, nitrogen elimination, and phosphorus reduction, combined with RO desalination and concentration, and MVR evaporation with drying and crystallization technology. This approach truly achieves "zero liquid discharge" of nitrogen and phosphorus wastewater, with all treated wastewater being fully recycled and reused.

2. How to prevent organic fouling of membranes?

In the "zero liquid discharge" treatment process for nitrogen and phosphorus wastewater, a certain amount of organic matter is always present. When these organics exceed a certain concentration or fall within a specific molecular weight range, they are particularly prone to causing membrane fouling. Membrane fouling by organics is an unavoidable challenge in wastewater treatment applications. TG Environment addresses this difficult technical issue by employing the combined AO+MBR biochemical combined process. This approach not only removes COD from the wastewater but also simultaneously nitrifies and decomposes part of the nitrogen and phosphorus, thereby reducing the nitrogen and phosphorus content in the wastewater.

3. Evaporation techniques for wastewater treatment

MVR (Mechanical Vapor Re-compression) refers to the process where secondary steam generated from evaporation (or distillation) − which has low temperature and pressure, making it unusable — is compressed using a compressor to increase its temperature and pressure. The steam is then reused as a heat source to heat the material intended for evaporation, thereby achieving the recycling of steam. This means the evaporation process does not require external steam input; instead, a small amount of electrical energy is used to obtain a significant amount of thermal energy, thus reducing the system's demand for external energy. MVR is an efficient energy-saving technology that maximizes energy utilization within the system.

After pre-treatment, nitrogen and phosphorus-containing wastewater enters the evaporator where it is heated using live steam. Once the heating reaches the operating conditions required for compressor startup, the compressor is activated to compress the secondary steam generated within the evaporator. This compressed steam is then recycled back into the system, significantly reducing the steam consumption. Meanwhile, the evaporator and circulating pump continuously circulate the feed liquid, facilitating evaporation and concentration; the concentrated liquid is then transferred to a concentrated liquid storage tank; next, it is pumped via a lift pump to a dryer for further concentration and crystallization. The condensate water is collected in a condensate water storage tank and is then used for the pure water system.

The function of the dryer is to further concentrate and crystallize the wastewater from the MVR process, ultimately forming solid salts. This transforms the waste into solid form, achieving zero discharge of nitrogen and phosphorus. The concentrated liquid from the MVR evaporator enters the distillation tank within the dryer for distillation. The solid residues produced during distillation are salts containing nitrogen and phosphorus. The secondary steam generated during distillation passes through a condenser, where it undergoes heat exchange and is condensed into condensate water, which is then collected in a condensate water collection tank. A recycling water pump is used to transport the condensate water to a reclaimed water tank for reuse in the pure water system.

In the field of energy conservation and environmental protection in China, the operational environment for water treatment is relatively mature, and the market space is very broad. However, when it comes to "zero liquid discharge" treatment of industrial wastewater, the investment is substantial and the costs are high, with room for improvement in treatment processes. As a result, there are very few enterprises that truly achieve "zero liquid discharge" of wastewater. TG Environment has continuously achieved breakthroughs and innovations in "zero liquid discharge" (ZLD) wastewater treatment technology, yielding very impressive results. Meanwhile, TG Environment ensures stable operations, low costs, and high efficiency. Through these advancements, TG Environment not only achieves the goal of water conservation but also effectively curbs the deterioration of water environments, thereby promoting coordinated development between industrial economies, water resource management, and environmental sustainability.