Low-cost and High-efficiency Ecological Sewage Treatment System

Introduction On October 4, the American Society of Landscape Architects (ASLA) announced the winners of the 2021 ASLA Professional Awards. GVL’s “Low-cost and High-efficiency: Use Low-Impact Development Facilities to Build an Ecological Sewage Treatment System for Remote Areas” won the Honor Award of Research Category. Over the past 21 years, GVL keep putting its effort in sustainable practice and technical research on Sponge City, trying to integrate the technology with landscape in each practice. This award-winning project is located in the central lake and surrounding area of Feilaixia Water Conservancy Hub, in Qingyuan city, north of Guangdong. which was led by Lvqiu Jie, the design director of GVL, has successfully integrated the Sponge City technology with landscape design. More importantly, it provides a "low-cost, high-efficiency" solution to the domestic sewage discharge problem in areas with remote locations and lack of funds. This article, contributed by Lvqiu Jie Team, will in-depth introduce the technology applied in Feilaixia Sponge Park. Let’s learn more about Feilaixia Sponge Park together with the chief designer, Mr. Lvqiu Jie. Feilaixia Sponge Park is located in the central lake area of Guangdong Water Conservancy Hub (hereinafter referred to as “hub”), which is remote with under-developed municipal infrastructure and without sewage treatment facilities around. As a result, the sewage from the research zone, office and living area on the site have been only treated with basic secondary septic tanks, and directly discharged into the pond of the park. The water quality of the pond has deteriorated year by year, which does not even meet the requirement for agricultural irrigation prior to the works. Meanwhile, the renovation was restricted due to a shortage of funds, which result in serious damage to the environment and biodiversity of the pond and surroundings. Therefore, a low-cost and high-efficiency sewage treatment system is urgently needed to properly discharge the sewage, improve the surrounding environment, and enhance the water quality and restore the ecological system as well. Moreover, users of the hub are seeking to a comfortable and ecological environment with low maintenance cost and high operational efficiency to solve both sewage treatment and stormwater management issues. Domestic sewage treatment in remote area was restricted due to its location and shortage of funds. The project was completed in 2018 and has been in operation for three years. Now the quality of water has been gradually improved, and the plants and environment have been restored, which provides a pleasant working environment for the staff of the hub. Based on the research objective, we teamed up with South China University of Technology (SCUT) and made an assumption that will replace the high-cost traditional engineering methods and used landscape strategies with "low maintenance cost and high operational efficiency" to solve the sewage treatment problems. The project aims to address: (1) What are the effective Low Impact Development (LID) facilities for sewage treatment? Can these approaches simultaneously act on the treatment of the surface water pollution caused by rainwater and domestic sewage? (2) How to effectively combine different types and proportions of Low Impact Development (LID) facilities under low cost constraints to achieve the optimal purification performance and achieve the goal of “Low cost and High efficiency”? Based on the questions above, we came up with three research plans: 1. 1. Focus on Low Impact Development (LID) facilities, plants and substrates to build a low-cost and high-efficiency sewage treatment system. 2. 2. Choose combinations in terms of construction cost, maintenance cost and the plant’s purification performance. 3. 3. Establish a sustainable landscape system from the perspectives of aesthetics, education and social influence. Combination of LID facilities, soil and substrates is the key to solve problems. 76%，15. 87%，71. We collaborated with specialists in the fields of sewage treatment, phytology and water conservancy engineering, and built models through field study, adaptive modeling Storm Water Management Model (SWMM) and orthogonal experiments, to quantitatively analyze and compare the wastewater treatment strategies of different Low Impact Development (LID) facility combinations in terms of construction cost, maintenance cost, substrate and the plant’s purification performance. When the four types of LID facilities including constructed wetland, rainwater wetland, wet pond and artificial floating islands, account for 4. 76%, 15. 87%, 71. 43% and 7. 94% respectively, the sewage treatment strategy has the optimal efficiency on the site. TEST: Plant selection and tracking of their growth TEST: Substrates selection and tracking METHOD: The runoff control rate, the removal rate of TSS (total suspended solids) and TP (total P) are simulated respectively on the SWMM platform, and the calculation of construction and maintenance costs are superimposed to determine the optimal combination mode to achieve Low-cost and High-efficiency. METHOD: According to the principle of the orthogonal experiment, four LID facilities are used as combination factors, based on which nine types of combinations will be simulated. The runoff control rate, the removal rate of TSS (total suspended solids) and TP (total P) were simulated respectively on the SWMM platform, and the calculation of construction and maintenance costs are superimposed to determine the optimal combination mode to achieve Low-cost and High-efficiency. 76%，15. 87%，71. Research Result: When the four LID facilities of constructed wetland, rainwater wetland, wet pond and artificial floating islands account for 4. 76%, 15. 87%, 71. 43% and 7. 94% respectively, the sewage treatment strategy has the optimal efficiency on the site. After completion, the landscape here is in a natural state and runs effectively without any human intervention except necessary maintenance, which nicely achieves our expectation. Based on the research conclusions, we first laid out two system on the site, respectively the sewage treatment system and the rainwater treatment system. These two systems are complementary and coupled. Rainwater can enter the sewage system to participate in the purification of water quality, and after sewage treatment, it can be used as a supplementary water source into the rainwater management system. The two work together to build a healthy ecosystem. In order to maximize the capacity of LID facilities on the site, the research team proposes two innovative design strategies which match with site characteristics based on the result of the research. 1. 1. To resolve the huge difference of elevation on site, the constructed wetland was designed as terraces. On the one hand, it resolves the height difference of 8 meters of the site, on the other hand, it maximizes the water body area, so as to maximize the decontamination efficiency, at the same time, it can also provide more potential for landscape opportunities. Constructed wetland is designed as terraces for efficient water treatment Secondary purification of waste water and rainwater from subsurface wetland 2. 2. To increase the contact area between the constructed wetland and the sewage, we introduced a brand-new vertical layout for substrates instead of the traditional horizontal layout, which proved higher efficiency in decontamination. A brand-new vertical layout for substrates is introduced to achieve higher efficiency in decontamination. To improve the living environment and upgrade the recreational experience, we introduced some landscape and artistic renovation and design, including: Gravel from local quarry used in ditch for both drainage and decoration purpose Permeable pavement made of recycle waste building materials collects runoff from the green land. Ecological design of external rainwater outlet The boardwalk dialogues with the wetland and provides a comfortable sightseeing experience. The purified rainwater in the wetland falls into the wet pond through the low weir trail Science popularization passage: a sponge system visiting tour route was carefully planned, showing the whole process of stormwater treatment to the visitors. garden decorated by a variety of selected local plants A landscape flower border formed by a combination of a variety of native plants The research project solved the sewage treatment problem of the site with a relatively low construction cost of CNY¥250/㎡, saving nearly 40% of cost compared to traditional engineering methods. At the same time, the original poor ecological sewage pond and its surrounding environment is transformed into a picturesque landscape garden and eco-friendly habitat. This research project demonstrates a “low-cost-high-efficiency" landscape strategy to solve the problem of sewage treatment in remote areas. The project has been promoted as a water ecological technology demonstration area and has received visits and attention from all over the country. It plays a role in science popularization and helps to raise the public ecological awareness. More importantly, this research is highly replicable and provides a universal solution for areas suffering from sewage issues all over the world, helping to improve basic living conditions in undeveloped and remote areas.