The worldwide demand for clean water for human, animal, crop and industrial consumption continues to rise, driven mainly by population growth, urbanization and industrialization. This is complicated by the fact that water quality in general is declining as a result of agricultural run-off, domestic sewage and industrial effluents. Evolving government regulations have also placed an enormous strain on the clean water supply by requiring greater water conservation together with more stringent levels of cleanliness. To further compound the problem, consumers are demanding greater quantities of available clean water at reduced prices.
The limited supply of clean water coupled with increased demand drives the need to develop new or alternative methods and solutions for water treatment. Depending on the type and nature of the pollutants, various gases can be used to purify water, such as oxygen, carbon dioxide and ozone. Each of these gases are particularly effective in dealing with certain challenges in water treatment in a cost-effective and environmentally friendly manner. The Linde group has developed various systems and solutions that are addressing these challenges.
Aeration brings water and air in close contact in order to increase the biochemical oxygen demand (BOD), which is the oxygen supply to the microorganisms that break down waste. The efficiency of aeration depends on the amount of surface contact between air and water, controlled primarily by the size of the water drop or air bubble. Insufficient oxygen causes many of the problems associated with wastewater treatment. Air is only 21 percent oxygen, so it may give rise to inadequate purification or even anaerobic decomposition processes, causing highly offensive odors, especially in warm weather.
The systematic input of pure oxygen at critical points along the wastewater chain solves the inherent problems of inadequate aeration quickly, flexibly and efficiently. Linde provides several processes for optimal oxygen transfer into wastewater using SOLVOX® gas dissolution systems (Figure 1). These systems can improve the performance of biological wastewater treatment plants effectively and economically, without the need for costly construction or restructuring work. The use of pure oxygen and a SOLVOX system enables low investment and maintenance costs while optimizing oxygen utilization.
Due to strict environmental requirements, wastewater may only be discharged into sewage pipelines or outlet channels if it is within a narrow pH range around the neutral point. While mineral acid treatment systems are effective in neutralizing alkaline waste streams, regulatory and cost factors are making carbon dioxide gas diffusion treatment systems an attractive alternative. Moreover, there are inherent safety issues in the handling of mineral acids, which are not present with carbon dioxide.
When dissolved in water, carbon dioxide forms carbonic acid, which reduces the pH value to the appropriate level. The use of carbon dioxide has many advantages over mineral acids.. It prevents excessive accumulation of salts such as chlorides and sulfates; in addition, it is virtually impossible to cause excessive acidification of wastewater because of carbon dioxide’s flat neutralization curve. Carbon dioxide is also much safer to use than highly corrosive acids and virtually eliminates corrosion problems.
The Linde SOLVOCARB® systems employ environmentally friendly carbon dioxide (CO2) to neutralize alkaline waters. The application equipment of the SOLVOCARB family can be applied flexibly in an in-line or bypass operation, thus offering a broad range of solutions to meet specific customer requirements. The SOLVOCARB portfolio includes reliable gas supply schemes and efficient injection equipment to perform neutralization and remineralization treatments with carbon dioxide.
Ozone is a colorless, unstable gas that forms a free oxygen atom that is highly reactive but short-lived. It is produced using an ozone generator. Ozone has a greater disinfection effectiveness against bacteria and viruses compared to chlorination. In addition, the oxidizing properties can reduce the concentration of iron, manganese and sulfur and reduce or eliminate taste and odor problems, so it is often used in drinking-water plants. This is accomplished by oxidizing the elements to form insoluble metal oxides or elemental sulfur removed through filtration. Organic particles and chemicals are eliminated through either coagulation or chemical oxidation.
Typical commercial ozone generators use a corona discharge process, where a high-energy electric field produces ozone. However, around 90 percent of the oxygen used in the process is not converted to ozone and remains unused at a high cost.
Leveraging its deep knowledge of adsorption processes, Linde created the patented OZORATM system, which efficiently separates ozone and recycles oxygen back to the ozone generator, reducing oxygen consumption by up to 60 percent (Figure 3). This technology has been jointly tested and validated with Suez, a leading manufacturer of ozone generators and a prominent player in the water treatment industry. This newly developed system effectively reduces the cost to produce ozone, opening the doors to expanded applications in water and waste water treatment.
Linde Group Overview
The Linde Group is a world-leading supplier of industrial, process and specialty gases. With over 30 years of experience in the field of water treatment and wastewater treatment, the Linde Group has been working together with plant operators worldwide to overcome critical challenges such as pH control, permanent and seasonal capacity increase need, odor control and micro-pollutant management. A more thorough description of the capabilities and benefits derived from the use of gases such as oxygen, carbon dioxide and ozone in water treatment processes may be found at lindeus.com.