This page has been prepared based on the principle of information sharing. In this section, which is structured in a question-and-answer format, emphasis is placed on inquiries received from factories, enterprises, various treatment companies, students, and researchers. Please send us any questions you would like answered. Questions and answers deemed valuable will be published on this page.
Question 1: How is chromium removed from wastewater?
Chromium metal can exist in two different ionic forms in wastewater: +3 and +6. Hexavalent chromium (+6) creates a highly toxic effect on microbiological activities. Hexavalent chromium is an anion and is usually in the form of chromate. It is possible to remove chromium chemically. First, hexavalent chromium must be reduced to the trivalent (+3) state. Then, trivalent chromium can be precipitated as a hydroxide compound. The reduction of hexavalent chromium to trivalent state is achieved by reacting tetravalent sulfur in a tank at pH < 3 with a residence time of at least 5 minutes. The mixer speed in the tank should be 2.5 – 3 revolutions per minute (within the tank). The reaction progress can be monitored via ORP (Oxidation – Reduction Potential). Sodium metabisulfite or sulfur dioxide gas can be used for tetravalent sulfur. Subsequently, in a separate tank, the pH value is adjusted to 8.5 using lime or caustic. Thus, the chromium in the wastewater settles to the bottom as chromium hydroxide.
Question 2: How are heavy metals removed?
Heavy metal removal from wastewater is based on the principle of hydroxide precipitation at high pH levels. Copper, zinc, nickel, and lead, which can be categorized as heavy metals, can be removed from wastewater with the help of lime or caustic in an average pH range of 10 – 11.
Question 3: How is sulfate treated?
Sulfate in wastewater is a significant problem, especially for factories dealing with acids (such as battery factories). Sulfate levels in battery factories can reach up to 13,000 – 15,000 mg/l. In the ISKI discharge to sewer regulations, there is a limit of 1,700 mg/l for the sulfate parameter. However, achieving this limit is often not possible through standard methods. Barium Chloride is the most well-known chemical for sulfate removal. Jar test studies should be conducted to determine the required amount of barium chloride.
Question 4: What is the phenomenon called Sludge Bulking in biological treatment plants and how is it controlled?
Sludge bulking is simply the excessive presence of filamentous organisms. These organisms cause biological flocs to bind weakly, leading to a situation where the sludge does not settle but instead “bulks” or rises. Filamentous organisms in the activated sludge process primarily consist of filamentous bacteria, Actinomycetes, and fungi. Common methods used to prevent sludge bulking include adding chlorine or hydrogen peroxide to the return sludge line, adjusting the Dissolved Oxygen (DO) concentration in the aeration tank, changing the return points to increase the F:M ratio, adding essential nutrients such as Nitrogen and Phosphorus, or using selectors.
Question 5: Do Wastewater Treatment Plants (biological) smell?
Yes, treatment plants can smell. The key is to allow for minimum odor formation. The primary reason for wastewater treatment plants to smell is unstable sludge within the system. If there is no separate stabilization unit for the disposal of excess sludge originating from the system, the treatment plant will emit odors. Therefore, a Sludge Stabilization Unit is required to reduce the odor originating from the treatment plant. Alternatively, a separate treatment system (gas/air treatment) can be considered for ambient odors.
Question 6: What does a Package Wastewater Treatment plant mean?
A package wastewater treatment plant is a portable, compact, and modular treatment system designed for domestic or industrial wastewater, specifically for small flow rates. They are generally manufactured from steel construction or polypropylene. ”Do you build package treatment plants?”. Yes, we build package treatment systems. For detailed information, please check the AKTİFPAK page.
Question 7: How much does a Wastewater Treatment Plant cost? I have a small textile workshop in ……..?
To calculate the cost of a Wastewater Treatment Plant, several factors must be clarified first: the flow rate of the wastewater, the characteristics of the wastewater, the location where the treatment plant will be built, and the type of material (reinforced concrete, steel construction, or polypropylene) to be used.
Question 8: Is domestic wastewater drinkable after being treated?
Domestic wastewater is highly rich in pathogens. Disinfection units are usually located at the discharge of domestic wastewater treatment plants, where chlorine is added to the wastewater. The disinfection efficiency of chlorine is 99.9%. If alternative disinfectants are used, this figure can reach up to 99.999%. However, considering that millions of viruses can exist even in treated water, it is clear that this level of disinfection is not sufficient to make the water drinkable for humans. Although rare, in a few places worldwide (such as the USA), the output of domestic wastewater treatment plants is disinfected with high-tech systems and fed back into the drinking water network following a signed consent from citizens. This situation is considered a viable response in regions experiencing severe drinking water scarcity.