By Huang Binrui, Li Yang, Mi Renzhi, Yang Shuo

Many Nanjing citizens may still remember such a view: when walking along the rivers in several residential areas in Nanjing, people had to cover their noses. Taking a close look at the rivers, many refuse collection stations were emitting dreadfully black liquid directly into the river, producing a horrible and disgusting smell. The view was easily seen before 2015. Back then, not only Nanjing was facing poor river quality and management, but many other cities in China were confronting the management problem of black-odor rivers. Fortunately, such a view is rarely seen in Nanjing now. Instead, now Rivers are cleaner and the landscapes are more eco-friendly; near the riverside, many elderly citizens chat with each other when doing some exercises every morning; intimate couples walk their dogs here together with smiles on their faces. You may wonder: how did the change occur? To be more specific, what technical methods and policies were carried out in Nanjing in so short a period from 2015 to 2021 to accomplish this feat?

Nanjing Rivers in the Past

Nanjing Pearl River is a historical and important river connecting the Xuanwu Lake with Qinhuai River. According to the government staff, before 2015, the Pearl River wasn’t as clear as today. Both the Nanjing government and citizens were not aware of the latent environmental issues previously, so no one was managing Nanjing’s urban water bodies in urban areas. But some problems were already emerging —- the rivers started to be filled with silt, stinky garbage, and black and turbid water; mosquitoes breed inside hence; nobody was willing to walk by those rivers. “Many residents would directly discharge trash as well as domestic wastewater from their own production into the rivers,” said government staff.

The First “Water Treatment Revolution”

Without supervision, the black-odor water phenomenon got increasingly severe, so the public had no choice but to report the situation to the government, hoping the government to respond… such voices of dissatisfaction quickly multiplied in 2015. As a result, the State Council initiated the water treatment “revolution.” by proposing the “Action Plan for Water Pollution Prevention and Control”, also known as the “Ten Policies of Water Treatment”. This document was soon adopted by the Central Political Bureau Standing Committee meeting. It proposes that five elements — regulation, marketing, science and technology, administration, and culture — should be joint together to establish a long-term mechanism for water treatment^[1]. The government staff stated: “Nanjing has been working hard to clean up black and smelly rivers since 2015. The Pearl River is an example. The water treatment for the Pearl River had two stages: first, engineering techniques, such as ‘Source Control and Sewage Interception,’ dredging, and river supplementary recharge, are used to address the most pressing black-odor issue. Then, ecological floating beds were placed in the river, and cultural decorations enriched the landscapes along the rivers.”

The water treatment techniques mentioned above reflected the contribution Nanjing has made when trying to figure out how humans can live harmoniously with the rivers. The increasingly systematic and intelligent water treatment strategy managed to establish itself as a viable method for Nanjing to achieve harmony between people and nature. Meanwhile, Nanjing continued to propel the “Rainwater and Sewage Diversion” project in the central urban area so as to make sure rainwater and sewage would go into separate pipes, which would reduce the workload of the sewage plants and therefore guarantee the water quality to a great extent. These procedures are carried out on many rivers in Nanjing that had the black-odor issue, and all the water treatment had been finished by the year 2020.

In solving the problem of black-odor, sewage treatment plays a significant role. After the introduction of “Ten Policies of Water” by the government, wastewater treatment technology has changed as a result of higher discharge standards. Taking Nanjing Gaoke Water Company as an example. Initially, the process adopted by Gaoke was Sequencing Batch Reactor Activated Sludge Process, or SBR. The SBR process takes up relatively little space and only one machine designed for SBR can serve many purposes. Due to the upgrade of national standards, Gaoke switched to A²/O process around 2014. The advantages of A²/O process are that it has a lower energy consumption, lower transportation cost, higher efficiency for the work of large sewage plants, and can achieve higher water quality after treatment.

Nanjing Water Treatment at Current Status

Behind the great progress, there are still some problems hindering the further improvement of water management in Nanjing.

In the first place, problems exist in the structure of infrastructural projects. Nanjing began laying rainwater and sewage pipes in 2012. Due to the design and aging problem of those pipes, however, the contribution of many sewage pipes is now a spent force. For instance, pipes previously paved in the Suojin Village, Nanjing have become extremely fragile, and some of the pipes can even go cracked when they are flushed by high-pressure water guns. If they are still in daily use, sewage will be very likely to flow to pipes other than sewage pipes and then leaks onto the ground, leading to greater issues.

On top of that, some policies aiming to alleviate the black-odor problem have clear inclinations, which leads to the discrepancies between the water management projects carried in different parts of Nanjing. A Nanjing citizen said with a sigh that “In urban areas, the black-odor problem is basically resolved, but in some suburban areas like Qixia District, many rivers are somehow left behind or ignored.” This reveals the uneven attention paid to the overall river management.

Moreover, the cost is also an inevitable problem, which limited the adoption of new and advanced technology. Many sewage plants are in a dilemma: there is now a newer and better process called Membrane Bio-Reactor, or MBR. This process is highly efficient and can produce water after treatment in high quality, but the membrane replacement operation needs to be done for each 3 to 5 years, and each time it can cost 30 to 50 million CNY. This deters many sewage plants, especially those that are not subsidized by the government.

Last but not least, the citizens’ awareness of environmental protection is not enough, which may lead to the re-occurrence of water pollution. Many of the restaurants and stores in older areas of Nanjing pay no attention to these environmental problems, so they just pour their wastewater and leftovers right into the sewage pipes, hindering the “Rain and Sewage Diversion” and added pollutants into rivers when contaminants have already exceeded the disposal limit. “Many companies were not cooperative during our inspection of illegal emissions,” said Greenstone Environmental Protection Center, a local NGO in Nanjing. These businesses did not want to face up their problems, so they use methods such as making excuses to delay the inspection again and again.

Looking to the Future with the Present in Mind

In 2020, the 14th Five-Year Plan was issued, which emphasizes sustainable and eco-friendly development. The future of river management is to achieve “eco-friendly water treatment” through the concept of sustainable development, thereby further promoting the harmonious coexistence between man and nature. The “sustainability” of water management has two aspects. The first is to turn trash into treasure. For example, the residual sludge from sewage treatment plants can be recycled. The second is to utilize and develop new energy. The 14th Five-Year Plan mentions the potential of sludge utilization. For instance, biogas produced by sludge after fermentation can generate power. Ideally, the electricity generated can relieve the energy burden of plants; What’s more, the harmless treatment is able to remove the harmful chemicals in the sludge, and then the sludge can be used in soil reconstruction. As for wastewater, the sewage source heat pump encourages the reduction of electricity consumption while stabilizing heating and refrigeration. Although these ideas are still in the experimental stage, they are worth investigating.

In the process of sewage treatment, a large amount of electric energy is necessary, and behind the huge consumption of electric energy, a large amount of CO₂ is discharged in the process of power generation, which is undoubtedly contrary to the concept of “sustainable”… the task of using new energy to replace electric energy is imminent. Nanjing Tiebei Sewage Plant has realized the use of laying solar panels to collect solar power generation as an auxiliary energy supply method. In the future, the use of new energy will be more and more extensive, and the replacement of electric energy is not far away.

Nowadays, big data has become an increasingly popular topic. In terms of river management, the development of smart technology has also become the future trend. The government and many local companies are not only working to build data sharing and automation, but also planning to combine big data with the current regulation to build an “intelligent water system”. The senior staff of the high-tech water company said: “Sewage treatment industry is a special industry. There should be no competition, but cooperation when solving the sewage problem.” The regulation system mentioned above has the potential to enable people to realize the global monitoring of water quality and report the problems in time. In addition, the system can optimize and automate every process in water treatment. More specifically, today’s aeration facilities need to be manually adjusted. If an automatic adjustment can be realized according to various indexes of the water body, the need for human labor can be decreased and resource waste can be greatly reduced.

Summary

From the aspect of technology and policy, Nanjing has made significant progress in water management: the visual and substantial change in black-odor rivers; the optimization of technology and efficiency in sewage treatment plants; the strong support from the government policies undoubtedly shows the great achievements made by Nanjing in water control, which makes Nanjing play a pivotal role in water control in China. With such tremendous progress, many problems are gradually being improved and solved, such as the unachievable technology breakthrough, the incomplete implementation of policies, and the structural problems of infrastructure. Experts and government officials are trying to address the root causes of these problems and solve them from different perspectives. With the introduction of new policies, river treatment technology is also developing towards a more eco-friendly, low-carbon emission, and energy-saving direction. The government is also trying to stabilize the details of the water management system and publicize the relevant knowledge among the public. With the improvement of people’s attention to water management and the protection of resources, “water management ” has been continuously promoted. It is believed that water management in Nanjing has a bright and promising future.

Reference:

1. Action Plan for Prevention and Control of Water Pollution. 2015.04.16. http://www.gov.cn/zhengce/content/2015-04/16/content_9613.htm

2. The 14th Five-Year Plan. 2021.06. http://www.gov.cn/xinwen/2021-03/13/content_5592681.htm

3. Implementation Plan for the Weak and Strong Items of the Short Board of Urban Domestic Sewage Treatment Facilities. 2020.07.31

4. Protecting the Quality and Supply of Freshwater Resources: An Integrated Approach to the Development, Management and Utilization of water resources. https://www.un.org/chinese/events/wssd/chap18.htm

5. Xinchao Zhang. Experimental Study on Sludge Drying System with Dual Heat Source Heat Pumps with Waste Heat Recovery [D]. Beijing University of Architecture and Architecture. 2020.

6. Jiweng Chang, Yuanyuan Jing, Yu Geng, Xiaotong Song. Promote the Low-Carbon Transformation of the Municipal Sewage Treatment Industry to Help Carbon Peak and Carbon Neutrality [J]. China Environmental Protection Industry. 2021, 4(06): 9-17.