Hardware

Introduction

In Macau water treatment plants, there is no enough equipment to deal with the emerging pollutants, such as nanomaterial, pharmaceuticals and endocrine-disrupting chemicals. However, with the development of technology, the amount of these emerging pollutants keeps increasing. One of the emerging pollutants in wastewater, endocrine-disrupting chemicals may cause cancerous tumors, birth defects or developmental disorders. If we don’t degrade Endocrine Disrupting Chemicals (EDC), it will make a deleterious effect on our health. Therefore, we go to visit the Macau water treatment plants and ask for support. We find that Macau water treatment plants seldom test the concentration of EDC because the wastewater only has extremely little EDC and the treated water is satisfied with the standard. Even though the treated water quality is good, we think we should improve our quality to make sure 100% no toxic to human.
In our project, we are researching cyanobacteria and laccase for degrading EDC. EDC is dissolved in water and most of their structures are hydrocarbons. Based on several types of research, laccase has exceptional degrade function and cyanobacteria has been widely used to be the protein production base. When we put laccase in water, EDC will react with laccase as the principle shows in the picture. After the reaction, those EDC will become water or a nontoxic inorganic compound. As a result, the water will be no hazardous to humans’ health.

As a result, we took one of the current biological treatment equipment as a reference with using genetic modification cyanobacteria in order to simulate the actual situation of sewage treatment.

Development of Model

Modelling of 1st Model using 3D Printer

As can be seen in the picture below, the 1st model is separated into two parts which are the red one and the blue one. The whole idea is to put the gene modification Cyanobacteria on the red discs and then insert the red discs into the blue filter. When the wastewater flows through the filter, water can react with the laccase released by Cyanobacteria. Since we wanted to show our product physically, we drew it using a software called SketchUp and printed it using a 3D printer. When we visited the Macao Water Supply Company, we showed our model to the staffs and they recommended that the efficiency of this model might be low and the wastewater can not fully react with the laccase while the wastewater passes through it. Moreover, they suggested us to have a look at the current biological treatment equipment, such as Trickling Filter and Rotating Biological Contactors.

Trickling Filter and Rotating Biological Contactors

During the process of biological treatment, one of the technologies is Biofilm Process; the organic matter is biodegraded by microorganisms attached to inert packing material. Normally, there are two types of equipment to achieve this process, which are Trickling Filter and Rotating Biological Contactors.

In Trickling filter, the wastewater is distributed to the permeable medium, which is consisted of the layers of rock, slag or plastic. In normal, layer of rock gives the void space less than 40%. Since the diameter of slag and packed plastic are smaller, the void space of these layers will be much smaller than rock layer. In addition, as the filtrate and solids will be generated during this process, there is an under-drain system to collect them and provide the air to the microorganisms on the filter. In the whole process, the better flow distribution can be achieved by cross-flow media.

The Rotating Biological Contactors can be divided into three parts, namely discs, a shaft and a trough. A series of discs are attached to the horizontal axis and they are partially or completely submerged in the wastewater. On the media’s surface, biofilm will be generated so that it can metabolize or degrade the organic materials within the wastewater. During its operation, the discs remain rotated by a mechanical motor or a compressed air drive, which can provide the oxygen to keep the aerobic conditions for biomass and make the contact between wastewater and biofilm better.

Their Advantages and Disadvantages

	Trickling Filter	Rotating Biological Contactors

Advantages	Little supervision, simpler operation No bulking sludge issues Ability to withstand shock toxic loads	Land requirement relatively small Easy construction and expansion Little supervision, simpler operation No problems with insects
Disadvantages	Sensitive to low temperature Large area of land required Lots of insects around Humus sludge	Difficult scale-up Slow process startup Low flexibility

Why do we choose to use rotating biological contactors

i. Land-use requirement

After more than four centuries of vicissitudes, Macao has gradually moved from a small fishing port on the coast of the South China Sea to urbanization, showing itself in the style of a modern small city.

In the long process of development and construction, it provides conditions for population growth. In other words, the development of Macau creates a variety of conditions for residents to live and work, so the number of people living more and more, the calm small fishing port is gradually buzzing. With the increasing population in Macau, the population density rises to 20,426/km2 and it becomes the most crowded city in the world.

Since there is a large amount of land-use requirement for buildings, it’s not a feasible solution to use Trickling Filters in Macau. Instead of using Trickling Filters, we may better choose Rotating Biological Contactors in order to make good use of the little area in Macau.

ii. Climate

Located on the west side of the Pearl River Estuary in southern China, Macau is the water and land junction of the Chinese mainland and the South China Sea. It is located south of the Tropic of Cancer and has opposite winds in winter and summer. It belongs to the monsoon region and climate classification. It is a summer rainy temperate climate. Macau has a long summer, and from May to September, which brings a lot of bad weather, such as heavy rain and thunderstorms. The waterspout also occasionally appeared. At the same time, from May to October, tropical cyclones frequently appeared. Compared to other European Countries, the weather is warm and humid in Macau, which is conducive to the growth of Aedes mosquitoes. The heavy rain increases the risk of mosquito-borne diseases such as dengue fever. Consider with easier for mosquitos’ growth in Macau, it will affect the efficiency of Trickling filter and the quality of the water treatment. Apparently, RBC is a better solution.

Factors Affecting Performance of RBCs

The performance of RBCs depends upon several design parameters apart from media. Particularly significant are:

Parameters	Effects
Rotating Speed	Mass Transfer of Nutrient and Oxygen in the Biofilm
Inlet Flow Rate	Substrate Removal Rate
Hydraulic Retention Time	Diffusion Rate of the Substrate into the Biofilm
Media	Affect the biofilm area and volume by different configurations or corrugation patterns of media
Temperature	Removal Rates of Organic and Nitrogen
Characteristics of Wastewater and Biofilm	The Biofilm Functions and the Relationship to the immediate aquatic environment.
Dissolved Oxygen Levels	Level of Producing Biomass
Medium Submergence	Bearing Loads of Equipment and Equipment Reliability

Modelling of 2nd Model using Laser Cutter

Components

Parameters	Dimensions
Length of the Trough	60cm
Breadth of the Trough	30cm
Height of the Trough	16cm
Volume of Trough	28800cm³
Number of Disc	10
Diameter of the Disc	20cm
Surface Area of the Disc	Around 180cm²
Submergence Level	Around 40%

After visiting the Macao Water Supply Company, we continued to search the information about the biological treatment equipment (Trickling Filters and Rotating Biological Contactors). Based on the analysis shown above, we finally decided to design our 2nd model taking the reference on Rotating Biological Contactors. When the wastewater passes through RBCs, the discs will rotate and react with wastewater. In order to increase the efficiency furthermore, we made some holes in the discs.

i. Better Reaction

While the wastewater contact with the laccase, they will react and degrade the EDC. Therefore, we create some holes on the discs of the Rotating Biological Contactor in order to provide more space to let the laccase and EDC react. As a result, we can put more Cyanobacteria bacteria in the Rotating Biological Contactors. Due to the better reaction, the efficiency of degrading EDC will increase. Based on this reason, it is possible to reduce the total size of the equipment which can solve the land shortage problem in Macau.

ii. Sustainability

Originally, there is no hole in the discs of Rotating Biological Contactors. Due to the above reason, we create some holes in the discs in order to increase efficiency. As a result, the material required to make the discs will be reduced. Therefore, the energy required to make the discs will be decreased and the whole process of making the equipment will become more sustainable and lower environmental impact.

Due to the size limitation of 3D printers, we used laser cutting to make the 2nd model bigger. The components of the model are drawn by CorelDraw, which is a vector graphics editor and made by the 3mm thickness poly-methyl methacrylate sheet. In order to further make the RBC model stick better, the Mortise Tenon Joint Structure is used.

Further Improvement

Until now, we have designed our model to degrade the EDC. In the next step, we will do the experiments to compare the degradation rate of EDC between our model, which has holes in the discs and a normal RBC, where there are no holes in the discs. In theory, the degradation rate in our model will be better. After the comparison, we will do a series of the experiment by changing different parameters which can change their degradation efficiency as discussed above, such as rotating speed, temperature, and medium submergence. Finally, we can get the optimal combination operation for providing the best performance on degrading EDC.

Team:PuiChing Macau/Hardware