The current situation and development trend of VOCs bio purification technology.

Biotechnology Channel News: In recent years, the large amount of volatile organic matter (VOCs) emissions caused urban haze, photochemical smog and other regional atmospheric environmental problems, seriously threatening human health and ecological safety.
May 2010, the Guidance on Promoting Joint Air Pollution Prevention and Control to Improve Regional Air Quality, forwarded by the State Council, for the first time listed VOCs as four key pollutants for air pollution control, together with SO2, NOx and particulate matter.
VOCs bioprocessing in the Netherlands and Germany, especially for medium and low concentrations of exhaust gas treatment.
biological principle is mainly the use of microbial metabolic activities, VOCs into cell metabolism of energy, cellular components and harmless small molecular substances (e.g. water, carbon dioxide, etc.).
advantages are: mild reaction conditions, simple equipment, easy operation, low operating costs, low secondary pollution, can handle different properties of mixed gases.
technology has been used on a large scale in Europe, according to statistics, the beginning of this century into operation of the device has reached 7,500 units.
of course, biological treatment technology also has certain limitations, mainly manifested in its limited rate of biodegradation, can not bear the load too high, the biological toxicity of the material treatment effect is poor.
, purification process.
bioprocessing process of VOCs and odorous exhaust gases mainly includes biofiltration cells, biodrop filter towers, bioscrubbers, membrane bioreactive devices.
, biofilters and biodrop filters are the most widely used, and membrane bioreacters are still limited to the laboratory research stage.
1, biofiltration In the biological filtration process, VOCs exhaust gas flow through pressurized pre-humidification, into the filter tower and filter layer surface biofilm contact, VOCs from the gas phase to the biofilm by the membrane microorganisms rapidly degraded and used, into their own biomass, water, CO2 and other small molecular substances.
biofiltration is suitable for a wide range of VOCs exhaust gas treatment, such as short-chain hydrocarbons, monocyclic aromatic hydrocarbons, chloroform hydrocarbons, alcohols, aldehydes, ketones, carboxy acid and sulfur- and nitrogen-containing organic matter, the typical applications include printing, spraying industry, sewage treatment and livestock farming industry.
The method is characterized by simple operation, low operating costs, wide range of application, do not produce secondary pollution, but the reaction conditions are not easy to control, easy to block, gas short-flow, trench flow, covers a large area, and slow adaptation to the change of air load.
2, biodrop filtration Biodrop filtration is an improvement of the biological filtration process, its bed fillers are mostly inert substances, compared with biological filtration, reduce the resistance of gas through the bed layer, due to continuous flow of liquid through the filling layer, so that the reaction conditions (e.g. pH) Nutrient concentration) is easy to control, the biomass per volume filler is high, more suitable for purifying the higher load of exhaust gas, while overcoming the characteristics of biofiltration is not conducive to the treatment of acid-producing exhaust gas, can effectively remove biodegradable acidic metabolites VOCs exhaust gas.
, it is reported that the biological drop filter reactor treatment of VOCs are mainly alkanes, olefins, alcohols, ketones, esters, monocyclic aromatics, halogenated hydrocarbons and so on.
the presence of a biodrop filter reactor due to the continuous flow of liquid phase, making the Henry coefficient larger pollutants not easy to remove.
3, biological washing biological scrubbers are also called biological washers, consisting of mass scrubbers and biodegradable reactors.
exhaust gas first enters the scrubber, with the inert filler microorganisms and mud water mixture from the bio-chemical reactor to absorb, absorb, some organic matter is degraded here, most of the organic matter in the liquid phase into the bio-chemical reactor, through the metabolic action of suspended sludge is degraded, bio-chemical reactor water into the secondary sink for mud separation, discharge, sludge reflow.
Bio-washing method is also known as bio-absorption method, in the course of operation, exhaust gas does not need to humidification, because the system consists of 2 independent reaction units, easy to control reaction conditions, low pressure loss, but its mass surface area is low, exhaust gas must be dissolved in the liquid phase, requires a large amount of oxygen supply to maintain a high degradation rate, and there is residual sludge, operating costs are higher.
4, membrane bioreactive device membrane bioreactive device is a new type of exhaust gas biological processing process, in the hollow fiber membrane bioreacter, the outer surface of the fiber membrane grows a thin layer of biofilm, suspension in the outer surface of the fiber membrane circulation, direct contact with the biofilm.
exhaust gas is dispersed from the bioreactive reactor air infested into each fiber membrane cavity, relying on the concentration gradient gas molecules through the membrane wall to the outer layer of the active biofilm degradation.
Its air flow and liquid flow on both sides of the fiber membrane, in the liquid surface of the fiber membrane formed a biofilm, which is larger than the surface area, high biomass, can remove excess biomass to prevent clogging, can add pH buffers, nutrients, co-metabolites and other promoters to the flowing liquid phase, can also exclude toxic or inhibitory products, maintain high microbial activity.
There have been some reports abroad of the use of membrane bioreacters to treat toluene and BTEX (benzene, ethylbenzene, xylene and toluene), although these studies have achieved good results, but the construction and operation costs of biofilm reactors are high, so that it is limited in the practical application of the treatment of VOCs exhaust gases.
the advantages of bioreactive devices, they are widely used in various industries.
biofiltration towers are suitable for handling exhaust gases generated in meat processing plants, animal farms, sewage treatment plants and composting plants.
Water Purification Plant in Zhuhai, China, used biofiltration tanks to treat odorous gases of 57,000m3/h and met the secondary emission standards.
biodrop filter tower has been successfully used in chemical plants, food plants, sewage pumping stations and other aspects of exhaust gas purification and deodorization.
Wang Qunhui , etc. used a biofiltration tower to carry out continuous pilot tests for more than 3 months on the main mixed exhaust gases such as butyl acetate, orthanol and phenylecetic acid, which occurred at the site of penicillin workshop of a pharmaceutical company.
washing towers are widely used in various industrial and municipal projects.
Yixing Co., Ltd. uses washing tower desulfurization, SO2 processing capacity of 24.5t/d, emission mass concentration of less than 100mg/m3.
and membrane bioreacters are used in relatively few industrial applications.
, the main factors 1, the biodegradability of exhaust gas components and water solubility is one of the main factors affecting the degradation performance of biological treatment processes.
traditional biofiltration/drip filtration processes are often considered unsuitable for dealing with difficult biodegradable and low water-soluble parts.
hydrophobic VOCs often result in lower biodegradation rates due to slower mass transfer rates from gas phase to water phase.
Deshusses, etc., with 17 common VOCs as the subject, established a method to evaluate the degradation capacity of VOCs of different properties, concluded that the removal ability of pollutants was related to the Henry coefficient and hydrophobicity, and found that the maximum removal capacity of pollutants followed the following order: alcohols and esters, ketones, aromatics, aromatic hydrocarbons and alkanes.
For the difficult biodegradable parts, some researchers take ultraviolet oxidation as a pre-treatment technology, biotechnology as the main purification process, through UV photooxidation pre-treatment, the difficult-to-degrade pollutants into biodegradable water-soluble substances, improve the treatment effect of subsequent bio-purification units.
Koh and other UV-treated alpha-ene gases, it was found that 50% of the degradation products are water-soluble, and the bioaturation of these products is 3 to 30 times that of alpha-ene.
Wang and others used a combined UV-biofiltration process to treat chlorobenzene and found that after 254nm and 185nm UV light treatment, the high concentration of pollutants was reduced to inhibit microorganisms, thus improving the removal efficiency of biofilters.
for hydrophobic parts, the previous generation mainly introduced hydrophobic organic phase in the reactor to strengthen the mass transmission of such substances, and thus improve its biological purification efficiency.
such as Van Groenestijn, etc., have reported that the removal load of positive hexane can reach 80g/(m3 ̇h) by introducing silicone into the biodrop filter reactor; Arriaga and others introduce the fungus Fusariumsolani and silicone in the reactor, increasing the maximum removal load of positive hexane from 110g/m3 ̇h )50% removal rate) to 180g/(m3 ̇h) (90% removal rate).
2, degradation bacteria microorganisms play a decisive role in the exhaust gas biological treatment system.
exhaust gas biological treatment device during the start-up phase of the filler layer to inoculated microorganisms.
inoculated microbiomes can be activated sludge, pure-species microorganisms specially domesticated and cultured, or man-made composite microbial microbiomes.
of the main research directions of this technology is to select excellent strains and optimize their living conditions.
addition, based on the metabolic characteristics of the bacteria, it is of great significance to artificially construct a complex microbiome with reasonable ecological structure to shorten the start-up cycle of the reactor, improve the competitiveness of the inoculated microorganisms and maintain the sustainable efficiency of the reactor.
There are many microbial populations that deal with VOCs exhaust gases, and the majority of the main body in the reactor are hetero-breeding microorganisms, mainly bacteria, followed by fungi, as well as lineworms and yeasts, as well as a small number of worms, worms and other protozoa.
Research found that in the process of biodegradation of exhaust gases, pollutant degradation is mainly related to bacteria, but the current research proves that fungi may become a more promising bacteria in the process of waste gas biological treatment, as a typical gas-based microorganism, it has a larger surface area, dry environment or strong acid environment has a strong tolerance, showing better removal performance of hydrophobic VOCs than bacteria.
changes in microbial community structure and metabolic function will have an impact on the macro-processing capacity of the reactor.
different reactor operating conditions, the formation of microbial community structure and dominant population is different.
methods for regulating the microbiome are: controlling the microennity within the reactor, inoculation with high-efficiency strains, or bio-strengthening.
traditional biotechnology is limited to the quantification and quantification of microorganisms.
with the development of molecular biology, some molecular biotechnology, such as denaturation gradient gel electrophoresis, fluorescent in-place hybridization, etc., have been used to study the structure and ecological characteristics of microbial community.
3, filler structure and characteristics Filler is the core part of the exhaust gas biological treatment device, its performance affects the adhesion of microorganisms and the operation of the system.
Ideal fillers should generally have the advantages of larger surface area, small filtration resistance, strong anti-blocking performance, suitable for microbial attachment growth, strong water holding capacity, small accumulation density, mechanical strength, chemical properties, long service life, easy access, low price and so on.
biological filtration method often uses organic active fillers as the main fillers.
commonly used organic active fillers are soil, compost, peat, diatom soil, bark, etc. or its mixture of which compost is most commonly used.
Organic active fillers have the advantages of low price, rich in nutrients and easy microbial attachment, but the organic matter of such fillers will gradually degrade mineralization, resulting in filler lamination and blockage, shorten the life of fillers.
, compound fillers made of organic and inorganic fillers are the focus of current research.
the bed layer of biodropping is composed of inert fillers, and the improvement and development of this kind of device is mainly reflected in the improvement and development of fillers.
traditional biological drip filter fillers have pebbles, rough gravel, charcoal, ceramic grains, volcanic rock, etc. , such fillers have low processing efficiency, easy to clog and other problems.
research and development of new biodropping fillers are mainly reflected in the continuous improvement of materials and structures, including: polyurethane foam, polypropylene balls, polyethylene balls, diatom soil, stainless steel, molecular sieves and so on.
The development of biological fillers is mainly to modifie known natural active fillers to improve the comprehensive performance of fillers or artificially increase the surface area and strength of fillers, improve porosity, reduce weight, prevent filler crushing and gas short-flow.
4, pH and temperature pH of spray nutrients is one of the main operating parameters affecting the bio purification performance of exhaust gases.
reaction system nutrient pH is mostly maintained between 5 and 8.
some studies have shown that lower pH (temperature) is one of the key parameters that affect bio purification performance.
microorganisms in the filling layer are mostly medium-temperature organisms, the bed temperature can be 10 to 42 degrees C, most experimental research and engineering applications of biological drip filtering/filtration system in the ambient temperature of 15 to 30 degrees C operation.
, however, many industrial emissions are higher than ambient temperatures, so conventional processes require pre-cooling of exhaust gases, resulting in increased operating costs.
to reduce costs, some researchers have studied the use of heatphilus in the biological treatment of exhaust gases.
the operating temperature of the heat-addicted bioreactive device is generally controlled at 45 to 75 degrees C.
Mohammad and other biofiltration treatment BTEX exhaust gas at 50 degrees C, its maximum removal load of 218g/ (m3 ̇h) (average removal rate of 83%) ;Deshusseses, etc. in 45 to 50 oC treatment of ethyl acetate exhaust gas, its operating performance is better than the same conditions of the medium temperature reactor; Luvsanjamba, etc., uses biodropping to treat a mixture of isodehyde and 2-ketone, resulting in a higher removal capacity at 52 degrees C than 25 degrees C.
, the research and development of the temperature-thymosinable bioreactive system is an important direction in the field of exhaust gas biore purification.
, the process of biological purification of exhaust gases is essentially the use of microbial metabolic activities to transform harmful substances into simple inorganic substances (such as CO2 and H2O) and cytoste.
the study of the process of biological methods to deal with organic exhaust gases has done a lot of work, but there is still no unified theory.
present, the more popular in the world is the theory of biofilm put forward by Dutch scholars, also known simply as "absorption-biofilm" theory, describing several steps: (1) the pollutants of exhaust gas first come into contact with water and dissolve in water;(2) Contaminants dissolved in the water phase, driven by the concentration gradient, spread to the biofilms around the medium, which are then captured and absorbed by the microorganisms in them;(3) Pollutants entering the microorganism are broken down as energy and nutrients in their own metabolic processes.
this basis, Sun Yushi and others put forward a new type of "absorption-biofilm" (double membrane) theory for the low concentration of organic exhaust gas biodegradation process.