Background

Part 1: The increase of copper production and other pollutants

With the development of industry, copper is in increasingly great demand in our society, thus
many countries are raising the production to meet the demands. ^[1] However, copper smelting, processing
and electroplating and other industrial production processes produce a lot of sewage containing copper ion and
some other contaminants, such as cyanide and fluoride. Pollutants of different sources of wastewater are listed in table 1. Copper ion, cyanide and fluoride are marked in red to highlight the severity of these three pollutants.

Table 1. Pollutants of different sources of wastewater

Sources of wastewater	Pollutants
Mining	suspended solids, acid, mercury, cadmium, arsenic, lead, copper, zinc, radioactive substance
Beneficiation	suspended solids, alkali, COD, cadmium, arsenic, lead, copper, zinc, fluoride, cyanide, sulfide
Heavy metal smelting	suspended solids, acid, alkali, petroleum, COD, mercury, cadmium, chromium, arsenic, lead, copper, zinc, nickel, fluoride, sulfide
Light metal smelting	suspended solids, acid, alkali, petroleum, COD, fluoride
Rare metals smelting	acid, petroleum, COD, fluoride, radioactive substance
Metal processing	acid, alkali, petroleum, COD, chromium, copper

1. The harm of water containing excess copper

Some people who drink water containing copper in excess of the action level may, with short term exposure, experience gastrointestinal distress, and with long-term exposure may experience liver or kidney damage. For people with Wilson's Disease, we strongly advise them to consult their personal doctor if the amount of copper in their water exceeds the action level.

2. The harm of water containing excess cyanide

CN^- is extremely toxic to fish. The minimum lethal dose for carps is 0.2 ppm. WHO (World Health Organization) stipulates that the intoxication limit for fish is 0.03mg/L free cyanide ions. Cyanide can enter the body via contacting with skin, cavity mucous membrane, inhaling, taking orally, injection, etc. After entering the body, cyanide dissociates into CN^-. CN^- can prevent Fe³⁺ from transforming into Fe²⁺, which causes the failure of a series of biochemical reactions, thus leads to the death of cells due to the shortage of oxygen. Meanwhile, the central nervous system loses its function rapidly due to the lack of ATP produced through respiration. Then the symptoms of respiratory muscle paralysis, cardiac arresting and multiple organ failure follow, leading to death promptly.

3. The harm of water containing excess fluoride

After fluoride entering human body, only half can be excreted via metabolism; the other half will accumulate in our body, mainly in teeth and bones. Excessive amount of fluoride inhibits the activity of some enzymes, damages the metabolism of calcium and phosphorus as well as causes serious diseases related bones (e.g. periosteum proliferation). It is also indicated that fluoride is a powerful central nervous system (CNS) toxin and might adversely affect human brain functioning even at low doses. In addition, even fluoride not directly untaken by human is dangerous. Fluoride not only has an adverse effect on plants, but also can be passed on through food chain, thus harming animals and humans.

Part 2: Weaknesses of current treating method

Copper ion

The main copper wastewater treatments include chemical precipitation, ion exchange, and electrolysis method. ^[2] As a result of the different production processes, the valence state and station of copper ions in wastewater have their own special properties. The Chemical precipitation method produces sludge containing heavy metal ions, which can cause serious secondary pollution. The Electrolysis method is inefficient and needs too much energy. The ion exchange method has a good extraction, but the high cost of the resin makes it completely unsuitable for an industrial process. ^[3] Treatment for different types of wastewater containing copper should be based on the nature of the wastewater. In order to meet emission standards, different process or combination of processes should be exerted for treating different types of wastewater. ^[4] Meanwhile, when dealing with wastewater containing copper, a very useful metal in industry, the recycle of it, should also be taken into consideration.

Cyanide

The choice of treatments for wastewater containing cyanide depends on the concentration of cyanide. For high concentration of CN^-, recovery method is applied; while for low concentration of CN^-, treatment method is used. Recovery methods include acidified alkali-aeration absorption method and steam desorption method. Treatment methods include alkaline chlorination method, electrolytic oxidation method, pressure hydrolysis, biochemical treatment, biological iron method, ferrous sulfate method and air stripping method. Unfortunately all these methods have some disadvantages that are unavoidable. The industrial process of some methods, such as the Acidification method, the chlorination method and the SO₂-AIR method, are very complex and cost a lot. The hydrogen peroxide method and the ozone oxidation method can't deal with some kinds of cyanate. Given the low degradation efficiency, further treatment is still needed after the electrolytic oxidation method or some traditional treatment like chemical precipitation.

Fluoride

Traditionally, there're two treatments for fluoridated water, specifically using lime to neutralize and precipitate F^- in water and using coagulating sedimentation with CaCl₂-lime.The problems of the two treatments include the demand for very large amount of neutralizer, the production of large amount of sludge, the difficulty in dehydration and the difficulty in reusing sludge. And both of the two treatments have high cost a limited processing capacity.

Part 3: Strength of our E. kungfu treating method

Our E. kungfu is capable of forming a biofilm, which can sense the specific heavy metal, and activate a cell surface display system that acts to remove and recycle copper ion. In addition, it has the amazing ability to degrade the main metallurgy pollutants, cyanide and fluoride, in wastewater directly. The rotating biological contactor (RBC) we designed makes this process more feasible. The disc rotates to let the biofilm touch the wastewater in a suitable rate, thus enables our E. kungfu to absorb copper ion, cyanide and fluoride effectively. Our method makes a great improvement based on current-biological treatments. It is highly efficient, low cost and reduces the secondary pollution.

Figure 1. Sewage with excess fluoride

Figure 2. Sewage with cyanide

Figure 3. The death of fish because of excess copper

References

[1] Chile May Raise Copper Production 13% To Meet Increasing Demand, Bloomberg
[2] Xu Xinhua, Song Shuang. Industrial wastewater pollutants treatment manual [M].Beijing Chemical Industry Press (CIP), 2000,264-266.
[3] Review of Copper Wastewater Treatment Technologies Song Chun-li, Chen Zhao-wen, Fan Hai-ming, Guan Ying-mei (The 718th Research Institute of CSIC, Handan 056027, China)
[4] The Current State of the Technology Treating Waste water Containing Copper. Lei Zhaowu, Sun Ying (Department of Environmental Engineering , Environmental Management College of China , Qinhuangdao Hebei 066004)