Soil Passage Water Purification. A conceptual design for Jiaxing, China

A conceptual design for Jiaxing, China

By Servaas Kievits and Vibeke van der Bilt

About our experience
To write a thesis is a great experience on its own but additional to the normal procedure, we got the experience of travelling to China. Doing a project on the other side of the world with such a great culture, that leads to cross sectional learning experiences.  It was without doubt the most meaningful period of our bachelor curriculum. We did not only learn a lot about the subject of our thesis, we were also able to meet many interesting people. We met professors of the water section in Beijing, phD students, contractors and engineers that were all very warm in welcoming us into their country. We were able see the real action during our visits to the different water treatment plants and got to know a little bit more about international cooperation and especially the Chinese way of engineering.

From the moment we arrived in China, it was a roller-coaster of experiences.  The first days we were still insecure about everything , but excited to start. The professors told us more about the complexity of our subject and everything we needed to know. From that day on our motto was: work hard, play hard. We spend a lot of hours in the library or in cafes working on the thesis during the week. We worked from early in the morning, mostly until midnight. That was our way of getting the most out of the experience, because than we had plenty of time in the weekends to enjoy China. Another philosophy of ours was:  ‘Learning a new Chinese word every day, and making a new friend every day’. This way we really pushed each other to meet new people and to get to learn more about the Chinese culture. One friend of us which we got to know via another friend was an extreme hiker. He took us to a forbidden section of the Great Wall. This was absolutely the most impressive day of our trip. We hiked hours in the wilderness to reach the Great Wall, and once we were there it was all left alone. Parts were all gone or overgrown, but with all the equipment we brought we were able to walk the Great Wall a few kilometers. Except for this experience, we also traveled to Chengdu, the city of the Jasmin tea, hotpots, eating rabbit heads and of course the center of the Pandas. Here we were also able to visit a drinking water treatment plant to learn more about their perspective on the subject.  Finally we travelled to  Shanghai to eat fried dumplings and drink a few Tsingtaos.  After this we took the high speed train back to Beijing and stayed one more week in the Hutongs, were we worked hard to finish our thesis.

We would really like to thank the Marc van Eekeren fonds for making this possible. It gave us a once in a lifetime experience and great friendships. It was really swang!

About the project
In the east of China, in the province of Zhejiang, Jiaxing is located. Jiaxing is a city with a population of over 4.5 million people. This many inhabitants of course put a severe pressure on the city’s drinking water supply. In this case, the current drinking water treatment plant (DWTP) does not suffice the needs of the people of Jiaxing. Especially in winter, needs in qualities can impossibly be met due to low bacterial activity, causing a product of the DWTP that does not meet the requirements for water quality of drinking water in China. Since the population of Jiaxing is growing, this will only worsen in the near future.

A possible solution for this challenging problem can be implementing a different way of abstracting source water. Whereas source water is currently obtained through wetlands after being abstracted from the nearby Yellow river, plans have been made to switch to or add a soil passage water purification (SPWP) step. This means that either infiltrated surface water (artificial recharge) or infiltrated surface water combined with groundwater (riverbank filtration) is abstracted. In order to determine and evaluate the best option for the drinking water problem of Jiaxing, we had to: 
i) Identify prerequisites for successful SPWP.
ii) Analyse the SPWP potential of the site in Jiaxing following comparable situations and their SPWP parameters.
iii) Implement the most suitable option for Jiaxing, based on analyses.

Prerequisites for successful SPWP are mainly geohydrological parameters as a good permeability, decent hydraulic conductivity, long retention times and a sufficiently large thickness of the aquifer. Sites in Zhengzhou, Deyang and the Netherlands were chosen to be analysed in order to quantify water quality parameters and to find links between the water quality and the geohydrology. To decrease the turbidity and ammonia levels in the product of the treatment plant, three different solutions were observed; Mixing in riverbank filtrate, adding artificial recharge and mixing of clean water were judged based on the suspended solids removal efficiency, NH4+ removal efficiency, costs, feasibility, use of space, consistency and sustainability. From these criteria it followed that addition of artificial recharge has the most potential to be implemented since it is less bound to local geohydrology and has the highest sustainability because it does not affect the environment and can be dimensioned for future water demands.

The proposed artificial recharge step consists of basically three main processes. From the effluent of the wetlands, the infiltration pond, sand bed and the abstraction wells for artificial recharge are placed. They are all given dimensions to fit the limited space. A wetland was removed to make way for a recharge pond and soil bed that consists of sand that meets all prerequisites but long retention times. Pathogens will therefore not be removed during artificial recharge but during the post-treatment. This post-treatment was designed from calculations based on water qualities from the plants in Zhengzhou, Deyang and the Netherlands. Cascade aeration, softening, rapid sand filtration, cascade aeration, activated carbon filtration and chlorine disinfection are all included in this post-treatment. After, the water flows to a clean water storage tank from where it can be directed safely to the city’s people.

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