As a typical nuisance pollution, odor pollution has received increasing attention in recent years. According to statistics, for four consecutive years, complaints about odor and odor in my country have accounted for more than 20% of all environmental complaints and nearly 50% of atmospheric environment complaints.

Odor pollutants and VOCs "grow from the same root", and their highly homologous attributes determine the necessity of coordinated governance between the two. However, the difficulty of odor elimination is much higher than that of VOCs treatment. As air pollution prevention and control gradually enters the subdivision field, how to build a complete odor pollution prevention and control system and propose effective solutions has become an urgent problem to be solved.

The "Analysis of National Odor/Odor Pollution Complaints from 2018-2020" shows that among the public's complaints about air pollution, the problem of odor and odor accounts for the highest proportion. In terms of quantity, from 2018 to 2020, the "National Ecological Environment Petition, Complaints and Reporting Management Platform" received 153,000, 111,000, and 98,000 odor complaints and reports respectively, showing a clear downward trend, with a drop of 39%.

"In recent years, units involved in VOCs pollution across the country have gradually tended to in-depth treatment, which has played a significant role in promoting the solution to the problem of odor." Wang Gen, executive director of the National Key Laboratory of Odor Pollution Control for Environmental Protection, spoke at the 8th National Odor Pollution Conference held recently. At the Pollution Supervision and Prevention Academic Conference, the reasons behind the data decline were interpreted.

However, a detailed analysis of the data shows that, in terms of the proportion of total complaints and reports, from 2018 to 2020, odor complaints accounted for 21.5%, 20.8% and 22.1% of all environmental complaints and reports, and the proportions fluctuate Upward trend.

In the final analysis, the public's tolerance for environmental problems such as stench and odor around them is getting lower and lower. As a prominent ecological and environmental problem affecting the public's sense of gain, stench and odor pollution need to be tackled urgently.

However, the prevention and control of odor pollution is not easy. Zou Kehua, director of the National Key Laboratory of Odor Pollution Control for Environmental Protection, told reporters that the supervision of odor pollution is very difficult, which is determined by the characteristics of pollution.

Zou Kehua said that the management of odor and odor pollution is faced with "three excesses and two few", that is, there are many complaints from residents, many industries involved, and many material components, but there are few effective supervision methods and few efficient control technologies.

First of all, the sources of odor pollution are very extensive, involving more than 50 industries, not only in the field of air pollution, but also in the field of sewage and soil, such as black and odorous water bodies, polluted soil, etc. In addition, there are many types of odor substances, which can be recognized by human senses at extremely low concentrations, making substance identification difficult and requiring high treatment efficiency; coupled with their transient and paroxysmal characteristics, it is difficult to capture polluted gases .

He said that at present, my country still lacks environmental quality standards and basic standards for odor pollution. Although my country promulgated the "Odor Pollution Emission Standard" in 1993, this standard has been unable to adapt to the current environmental problems of odor and odor. In the above-mentioned meeting, many experts called for revising the standards, improving the quality, emission, monitoring and other standards, and building a system of odor prevention and control standards.

In addition, since bad odors are judged by people's olfactory perception, "standard pollution" is also one of the common difficulties.

Chai Fahe, deputy director of the National Joint Center for Air Pollution Prevention and Control and former vice president of the Chinese Academy of Environmental Sciences, said that how to more accurately judge odor pollution and use the public's perception and description of odor as the standard limit value still requires technical knowledge. support.

The bad smell must not only meet the "national standard", but also meet the "civilian standard", which has become the consensus of the participating experts.

At present, in some VOCs treatment plans issued by the state and local governments, they all emphasize the focus on VOCs treatment and collaborative treatment of stench and peculiar smell.

Zou Kehua explained that this is mainly because the odorous substances and VOCs are mostly of the same origin. Most of the malodorous substances belong to volatile organic compounds, and at the same time, most of the volatile organic compounds are also odorous. In the process of air pollution prevention and control, while reducing the total amount of VOCs, it also reduces the concentration of odorous substances, achieving the purpose of collaborative governance.

But he said that malodorous substances also include inorganic gases and semi-volatile substances, such as hydrogen sulfide, ammonia, phthalates, and anilines. Some industries have low VOCs concentration but prominent odor problems, such as garbage treatment, sewage treatment, livestock and poultry breeding, food processing industries, etc.

"Therefore, whether VOCs can achieve coordinated management of odor pollution after in-depth treatment requires specific analysis of specific issues." Zou Kehua said.

The odor threshold of some odor pollutants is extremely low, which means that the elimination of odor is much more difficult than VOCs treatment. However, the current governance level of enterprises involved in odor and odor is relatively backward, especially in some industries that are not dominated by VOCs. Zou Kehua explained: "These enterprises generally lack control requirements for air pollution prevention and control, production is still very rough, and the problem of odor pollution is also relatively prominent."

At present, the treatment technologies for bad odor include absorption method, adsorption method, biological method, plasma/photooxygen method, and combustion method. "It is basically similar to the VOCs treatment technology of many companies at present. The treatment efficiency is related to the industry. Some industries can reach 70%-80%, and some industries only have 20%-30%." Wang Gen added.

Similar to enterprises with low efficiency of VOCs treatment, enterprises with low efficiency of odor pollution treatment also have the problem of insufficient operation and maintenance of facilities. Wang Gen told the reporter: "During the investigation, it was found that the production facilities of the enterprise have leaking, leaking and leaking phenomena, causing the smell to escape; the airtight collection facilities are old and ineffective, such as the collection pipeline is damaged; there are many cases of non-regular maintenance and inefficient operation of the treatment facilities, For example, the amount of activated carbon is seriously insufficient, the activated carbon is seriously blocked, and more than half of the lamp tubes of the photooxidation device have been damaged.” He said that relevant companies should still raise their awareness, adhere to the main responsibility, and solve the problem of fugitive emissions in a timely manner. From the source of production facilities Controls odor escape.

At present, the country pays more and more attention to odor pollution.

In November 2021, the "Opinions of the Central Committee of the Communist Party of China and the State Council on Intensifying the Battle of Pollution Prevention and Control" clearly stated that efforts should be made to control stench and odor. According to Zou Kehua, at present, more than 20 provinces and cities across the country have incorporated the prevention and control of odor pollution into the requirements of the "14th Five-Year Plan", and the relevant prevention and control requirements are gradually refined.

"The overall trend we observe is that from the very beginning, the general requirements for the prevention and control of odorous gases have changed to the detailed and clear requirements of setting reasonable protection distances, strengthening the monitoring and early warning of odorous electrons, and strengthening scientific and technological research." Zou Kehua, Shanghai Cities such as Beijing and Tianjin have issued emission standards for odor pollutants, and some provinces and cities have also formulated emission control requirements and recommendations for prevention and control measures for specific industries.

For the next step of my country's odor pollution prevention and control, Zou Kehua suggested that it can be divided into three steps. The first step is to find out the bottom line and focus on governance. Taking complaints as the starting point, sort out key regional enterprises and key parks, establish a hierarchical ledger, and rectify key complaint parks and companies;

The second step is to establish regulations and comprehensive rectification, study and formulate odor pollution prevention and control policy documents, improve the standard system, carry out training and assistance guidance, promote comprehensive rectification of various industries, and strengthen pollution supervision of parks and enterprises with frequent complaints;

The third step is to assess management and consolidate results, formulate a performance evaluation system for odor prevention and control, incorporate odor into urban air quality assessment indicators, promote informatization and intelligent supervision, improve complaint response capabilities, and consolidate governance results.

When it comes to governance methods, Wang Gen added suggestions to strengthen classification and rectification. He said that industrial sources can be divided into two categories. VOCs-dominated industries have generally carried out VOCs remediation, but some low-olfactory threshold substances still have an impact. According to the characteristics of the industry, further in-depth purification treatment can be carried out for enterprises involved in odor complaints to meet the "civilian standard" requirements.

For industries dominated by odor, the concentration of VOCs is generally low, mainly due to the problem of odor and odor, and the level of pollution prevention and control is relatively weak. The focus can be on strengthening unorganized emission control, strengthening closed collection, identifying odor-causing substances, and screening feasible treatment technologies .

For agricultural sources, since the stench is concentrated in the pens and manure treatment links, the air volume is large, and the construction and operation costs of acceptable treatment facilities are low. It is necessary to combine large-scale livestock and poultry farming ammonia emission reduction pilots, strengthen the research on efficient and low-cost deodorization technology, and explore the collection and treatment of small-scale farms and free-range households.

Living sources are close to residential areas and are greatly affected by management levels; municipal sources are large in volume and cover a wide area, making closed collection difficult. These sources can be combined with garbage classification, strengthen the sealing and odor collection and treatment of garbage transfer stations, promote the conversion of landfill to incineration, and strengthen the prevention and control of odor in waste incineration plants, especially the odor collection and treatment in unloading halls and leachate treatment stations.

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