Complete solutions in wastewater treatment at gas plants

The specialists of engineering company ENCE GmbH together with the leading European ecological institutes develop unique technologies of industrial wastewater treatment for needs of gas treatment plants and chemical enterprises to order. Units and complexes are developed to specific requirements of a customer. Units are equipped with the equipment of leading global manufacturers.

Utilized treatment technologies ensure discharge of treated water into the field ponds or its utilization in a closed loop of the enterprise.

Main utilized technologies:

• Mechanical cleaning;
• Chemical cleaning;
• Pressure flotation;
• Membrane cleaning;
• Chemical reagent treating methods;
• Electrochemical neutralization;
• Ion-exchange treating methods;
• UV treatment;
• Techniques based on surface active substances, etc.

The company develops its systems and plants based on the following methods (see below). The choice of the method depends on pollutants composition and type, their concentration in the waste water and local technological environment.

At the preliminary stage of waste water treatment, mechanical treatment of various kinds is used. Bulky sand wastes and other suspensions are removed during this stage. Mechanical purification is a preliminary stage that helps to prepare industrial and sewage wastes to further treatment. At this stage, various systems and modular plants can be offered depending on the requirements to further treatment.

Mostly widespread standard solutions:

• gratings of various type and with various flow passage sizes
• sand catchers (horizontal, vertical etc.)
• separators — compact modular plants providing up to 95% of suspensions removal with particle size up to 0.2 mm.

The construction of the plant is chosen on the basis of wastes component analysis, required purification rate and customers’ requirements to the dimensions of the plant.

The offered technology is based on the emulsified product release from the waste water flow.

First of all, a coagulating agent is injected into the waste water that is being treated. As a result, emulsified substances that have previously been insoluble become precipitated. Once the flocculant is added, it enhances aggregation of the suspended particles and they break.

Coagulant and flocculant are added by means of specific instruments — coagulators and mixing chambers. These also carry out water treatment at the preliminary stages.

During the next treatment stage the flocculated precipitate is released by means of sedimentation, flotation or another separation technique.

The plant is completed with a specific type of flotation machine depending on the sediment characteristics.

Plants can be completed with the following types of flotation machines according to technical requirements:

• piped flotation machine
• capacitive flotation machine

Flotation machines are additionally completed with metering pumps, feed stations, mixing stations and machine monitoring systems.

One of the major processes that allow extracting hard-precipitable emulsified suspended materials and products from the polluted sewage water is flotation. The process can be carried out in several variants depending on existing technical conditions and pollution type:

• induced air flotation
• free-flow flotation
• vacuum flotation

Flotation process consists in the extraction of foam precipitation to the water surface and its further collection. The precipitation is generated after the purification.

During preparation prior to the flotator treatment, water is being mixed with coagulants and flocculants. After that it enters the lower part of the machine and goes under the sparge tube. Air-water mixture, formed with purified water and air from ejector, is simultaneously fed to the sparge tube.

As a result of this collision of the flows, air bubbles cling to flocculent sediment that is being released at coagulation/mixing chambers and extract the sediment to the surface. It is removed from the surface by means of movable cleaning scraper and placed into a storage hopper. Flotation is considered to be one of the most effective methods for the extraction of hard-precipitable, emulsified or dissolved pollutants.

Our company offers various assemblies of induced air flotation plants:

• standard radial flotator in the concrete casing for highly-effective purification of sewage and industrial water by means of induced air flotation. Water for further purification can be taken from various plants, including those from municipal services sector, where suspended matter rate can reach 6000 mg/l.
• rectangular flotator is a compact space-saving modular plant designed with components quantity reduced to the minimum. This structure does not require a pressure reservoir while loading wafer pack allows using working space as effectively as possible. Maximum depth may reach 98%.

If the flotation is complicated due to the considerable heavy particles content, additional subsidence is used. If the Customer needs water purification rates to be even higher, a plant that combines sediment flotation and purified water filtration can be used. This plant consists of a coagulation chamber, flotator and a double-layer sandy-anthracitic cell-type filter (17–27 cells) with intermittent flushing of each cell. During the plant performance, water undergoes flocculation, flotation and then filtration through the double-layer cell-type filter (sand /anthracite).

Intermittent filter flushing is implemented section-by-section by means of backwash method. Rinsing water returns to the coagulation chamber for purification. While one of the cells is being flushed, water is filtrated through the rest. Height of the filtering bed component — 1.5 m. Water layer thickness is 400 mm. The amount of circulating water is 10–20% of the whole volume of the water to be purified.

So that to meet more demanding requirements to water treatment standards, mineral coagulants and flocculants can be used on all plants. Flotation plants can also include pumps for flow supply to the plant, air treatment stations, etc. Both standard control panels and individually designed ones (in compliance with requirements’ specification) industrial control systems are optional.

Aeration tanks are the most widespread industrial solutions for sewage water treatment at the industrial treatment plants that use traditional biological treatment. These tanks require much space, additional disinfection (ultraviolet treatment, chlorination) and generate offensive odors. Besides, the quality of the treatment is changed because of sewage water input parameters’ fluctuations.

Treatment solutions on the basis of membrane technologies offered by our experts allow reducing building costs up to 70%, whereas the quality of treatment gets much better. Bacteria and almost all the viruses are removed. The purified water meets German requirements to swimming pool water quality.

Membrane ultrafiltration plants help to solve the problems of traditional sedimentation tanks with substances floating on the water surface as well as problems with the removal of sedimentation buildup.

Existing primary and secondary settling tanks can be converted into buffer tanks.

Membrane bioreactor is a composition technological process that combines biological stages of sewage water treatment with membrane filtration. The technology integrally consists of 2 purification stages:

• biological treatment
• membrane filtration

Mechanical pre-treatment plays an important part as well. A sieve of perforated sheet, mesh O = max. 3 mm with additional standby filtering screen is used for mechanical treatment. Its additional filtering screen prevents untreated sewage water from entering the treatment system. Mechanical pre-treatment removes fluffy and other fibrous components that can clog or damage the membrane made of hollow fiber during the next treatment stage.

Once the pollutants are removed by means of mechanical filtration, sewage water enters a bioreactor for biological treatment. It is carried out via a series of time-controlled step-by-step reactions. Two or more bioreactors are usually used in the system; they perform as a series reactor of intermittent action. However, unlike traditional reactors of intermittent action, membrane bioreactor system does not require series of sedimentation and decantation. It enhances active sewage water treatment in each bioreactor for the whole decontamination cycle. The final stage of the membrane bioreactor process is the direct filtration of suspended materials at the mixed solution by means of ultrafiltration membranes located in a separate reservoir. As sewage water is filtrated by the membrane, pure water (filtrate) is received at the system output, whereas suspended particles in the mixed solutions concentrate in the membrane reservoir/reservoirs and constantly return into bioreactors.

Membrane bioreactor is a unique time-controlled process where interchangeable ventilation is used in order to support nutritive substances removal at a simplified process. Inbuilt immersed membranes ensure direct filtration of a large concentration of suspended solids at the mixed solution. This process ranks the membrane biological treatment system with high-quality coupled biological reactors of unique class.

Application range:

• sewage water processing
• contaminated water treatment
• ground waters back pumping (reinjection)
• water treatment — ideal for further processing via reverse osmosis
• industrial reuse reducing fresh water consumption
• modernization and treatment process development

Typical layout

1. Biological process
   Filtrated water enters the biological system and undergoes time-controlled processing. Ventilation is provided by means of replaceable diffusers and independent mixing is used for energy conservation. It also helps to achieve the required reactor conditions. Effective treatment can be carried out either at real-load operating mode, or at continuous flow mode.
   
   Real load process:
   The flow enters a reactor at the specified time and the flow smoothes out during ventilation and mixing of the reactor filling phase. Ventilation and mixing continue in the other reactor and the sediment is pumped over to the membrane reservoirs during reactor discharge phase.
   
   Continuous flow process:
   As the flow enters, the water level of the reactor is maintained at almost constant level and is discharged from all the reactors simultaneously.
2. Membrane filtration
   Sediment generated after the biological process continuously enters membrane reservoirs. Membranes are immersed directly into the biological solid particles and the filtration is carried out uniformly by all the membranes. Excessive biological solids either return to the reactor, or are removed from the system.
3. System control
   A simplified disposition of pumps and blowers is used to discharge the purified waste water and to support membrane water-resistance. Backwash, oxygenation treatment and chemical treatment are carried out automatically controlled by an operator at the plant.

Bioreactor

• Simplified requirements to pre-treatment via filter screen
• Enhanced nutrients removal
• Time-adjustable control offers unlimited flexibility when working with several reservoirs
• Separate pumps for nitrate recirculation
• Real time control system for oxygen needs and proportional loading
• Inbuilt alignment minimizes membrane zone
• Controllable sediment recirculation from the membrane reservoirs prevents dissolved oxygen from penetration during the oxygen-free treatment
• Predictable analysis of membrane feed allows planned backwash and full discharge

Advantages:

• the system offered is ideal for limited space conditions
• modular design supports the applicable expansion
• the lowest energy consumption among MBR systems
• high reliability along with membrane filtration
• high level of suspended materials in the mixed solution for volume decrease or sediment stabilization
• pressure barriers prove high-quality water treatment even under the conditions of severe load
• a quick solution for the plant expansion.

Environmental needs and increasing environmental concern may raise the application of UV sterilizing systems at sewage treatment plants up to 70% in comparison to chlorination (in the domestic market). It may happen due to the fact that UV treatment does not generate disinfection byproducts. Nowadays UV treatment is used on all kinds of sewage treatment plants, from small automatic country ones to the large ones. UV treatment application also became more diverse which means that it was generally approved as an effective and saving way of sewage treatment.

Ultra-violet light is a natural component of electromagnetic spectrum. It is located to the left of the visible radiation with higher energy levels and wave length of 200~400 nm. UV treatment destroys bacteria, viruses and other contaminants using the same principles as the sunlight. Direct sun rays constantly purify the water, thus making biological impurities inactive. The light used in the UV system is generated by the mercury arc lamps. Each lamp is surrounded by a water-resistant quartz tube. Typical initial wave length from an average pressure lamp is approximately 265 nm, while that of a low pressure lamp is 253.7 nm.

Intensive UV light approaches microorganisms in the water and influences their DNA directly. Once DNA is deactivated, cell division stops. Destruction of more than 99% of pathogenic germs is possible.

UV system has more effective performance characteristics than traditional chlorination. Chlorination requires 15–30 minutes for the appropriate performance, while UV treatment requires just several seconds on the discharge line which means that the single flow price from UV is very low.

Due to the fact that plants do not always have an opportunity to remove the piling up waste from wastewater treatment facility to a waste burial site, we can optionally complete sewage water treatment unit with a sludge dewatering unit. It will carry out a finishing stage of waste water treatment and allow future sludge utilization. Our company can develop, complete and deliver dewatering, drying and combustion plants for sludge processing. This technology allows receiving end product with less than 10% dampness at the output.

Sludge processing consists of three stages:

On the first stage, a division between liquid and solid phases and preliminary dewatering occur. Dewatering is carried out on the pressure filters (screw or belt).

Final dewatering and drying take place during the second stage. The residual moisture is being removed in the special chambers at relatively low temperatures. Output moisture percentage varies from 30 to 8%. Various types of gas, steam and even hot water can be used as heat-carrying agents.

During the third stage, dried and dewatered product is being formed into the granulated material. It is abrasion-resistant and easy to store. Its burning characteristics can be compared to that of brown coal.

The granulated material received can be processed or burnt in order to generate electricity.

Depending on the customer’s requirements we can offer closed cycle of waste water treatment and sludge processing with almost zero emissions.