When it comes to pollution, the first thing we think of is sewage, bad factories discharge sewage into rivers and other news, but in fact, what we have not paid attention to is sludge.
    At this year's National Two Sessions, many delegates pointed out the problem of sludge, which instantly pushed the problem of sludge treatment to the forefront. Now our country's urban sewage treatment scale has reached 220 million tons per day, and the daily production of sludge with a moisture content of 80% exceeds 60 million tons, and it is expected that by 2025, the annual output of sludge will exceed 100 million tons. If this tense continues, the problem of sludge treatment will be the problem that hinders the last mile of sewage treatment.
    1. The sludge problem is said every year but it is there every year, and the root cause is it!
    Water quality and sludge treatment and disposal are important factors affecting the stable operation of urban sewage treatment plants in our country. With the advancement of pollution prevention and control, our country's sewage treatment rate has exceeded 90%. In contrast, the harmless disposal rate of sludge is less than 30%. It can be seen that the problem of heavy water and light sludge has not been solved for a day or two, and the sludge problem has not been solved.
So what is the reason for sludge problems every year? Is it just the concept of heavy water and light mud?
    Professor Wang Hongchen, director of the Low Carbon Water Environmental Technology Research Center of Chinese University, conducted a survey of 467 urban sewage treatment plants across the country and found that more than 67% of them had a sludge concentration of more than 4000mg/L, more than 45% of the sewage treatment plants had a sludge concentration of more than 5000mg/L, and nearly 20% of the sewage treatment plants had a sludge concentration of more than 7000mg/L.
    In our country, three disposal methods are usually adopted: sanitary landfill, building material utilization after thermochemical treatment, and land use after biological stabilization treatment. However, all three directions have varying degrees of problems:
    Landfill is better than dumping at will, but there are fewer and fewer sites available for landfill, and we often encounter the embarrassing situation of "no land to bury";
    Incineration is better than landfill, but the moisture content of sludge is high, the energy consumption of incineration is too high, and the neighbor avoidance effect is serious.
    Land use is better than incineration, but the sludge has higher requirements and needs to be stabilized. Due to the adulteration of industrial wastewater, toxic and harmful substances such as heavy metals in sludge often exceed the standard, and land use is restricted.
    According to incomplete statistics, only a small part of the sludge in our country's urban sewage treatment plants has been stabilized for land use, incineration and use as building materials, and most of the sludge has not been standardized.
    Therefore, the treatment and disposal of sludge is a key issue hindering the field of sewage treatment. So where is the bright road for sludge treatment and disposal?
    2. Four mainstream technical routes, sludge treatment and disposal are expected to "run"!
    After years of exploration, according to the characteristics of low organic matter content, high sediment content and large yield of sludge in our country, four mainstream technical routes have been formed: deep dehydration + emergency landfill, anaerobic digestion + land use, aerobic fermentation + land use, dry incineration + ash landfill/building materials utilization.
   These four mainstream technologies are not perfect at present, but if they can be adapted to local conditions, combined with the company's own situation and external environment, and how to deal with it according to the land conditions and economic development conditions of different regions, these four technical routes are currently feasible.
   At the same time, sludge is an organic solid waste with high water content and easy perishability. Improper treatment will cause secondary pollution to the environment, so the treatment link should include two important links: "stabilization" and "resource utilization". However, organic fertilizers have been banned, sludge moisture content is high, transportation and treatment costs are high, and it is difficult to collect township sewage treatment fees. It is very difficult for some underdeveloped regions to rely on public finances to bear the burden. Therefore, the high resource utilization cost of sludge treatment is the main problem faced by sewage treatment plants.
   3. Sludge is "eaten dry and squeezed clean" to achieve 100% utilization
    Sewage treatment turns sewage into clean water and purifies urban water resources. However, sewage treatment derivative sludge has always been a difficult environmental problem to solve.
    Wuhan's sewage treatment plant has tried a variety of methods to treat sludge: landfill, composting, and brick burning, but the results are not good and the sludge cannot be treated 100%.
Is there a way to solve the sludge without "sequelae"?
    In 2007, Huaxin Cement Company began to seek environmental protection transformation and established its first environmental protection company - Huaxin Environmental Engineering (Wuxue) Co., Ltd. Through research, Huaxin Cement Company found that the organic matter in the sludge can replace coal as fuel for making cement.
   "The method of using mud cake as fuel has achieved 100% recycling of sludge." Zeng Yizhe told reporters that municipal sludge contains 50-60% organic matter, and its dry base calorific value is about 40% of coal, which can replace part of coal burning in the process of collaborative disposal of cement kilns. The composition of the burned ash is similar to the raw materials for cement production, which can be used to make cement, "which means that the sludge is used as fuel without any residue, and it is really eaten dry and squeezed." ”
4. To fully realize the harmless disposal of sludge, there is a long way to go and it is imminent!
   The "14th Five-Year Plan for the Development of Urban Sewage Treatment and Resource Utilization" clearly states that by 2025, the harmless disposal rate of urban sludge should reach more than 90%, and by 2035, the harmless disposal of sludge will be fully realized, and the level of resource utilization of sewage sludge will be significantly improved. Therefore, it is urgent to promote sludge treatment, so how can we effectively promote the treatment and disposal of sludge in sewage treatment plants. In the middle of this year's two sessions, Hanfei put forward the following three suggestions:
    1) Carry out the evaluation of sludge treatment and disposal effects
      At the national level, the state organizes forces to carry out special investigations on sludge treatment and disposal, comprehensively assess the actual effect, existence and potential risks of sludge treatment and disposal, improve sludge treatment and disposal standards, optimize the technical route suitable for our country's national conditions, and formulate a negative list to prevent the transfer of pollutants between the gas phase and the solid phase (slag) during the collaborative treatment and disposal of sludge. Rationally study the effective destination of sludge recycling, break trade barriers, formulate national standards for sludge recycling, force urban sewage treatment plants to enter water according to standards (industrial wastewater related to sludge recycling is not allowed to enter), and take the opportunity to trace the source of pollution through the characteristic factors in sludge, so as to effectively promote the high-quality operation of urban sewage treatment plants in our country. Environmental protection supervision and inspection at all levels shall clarify the specific content and standards of sludge treatment and disposal supervision and inspection as mandatory and key matters.
    2) Formulate special plans and action plans for sludge treatment and disposal
      All localities should formulate special plans for sludge treatment and disposal, investigate sludge stock in detail, accurately predict sludge increment, systematically lay out sludge in their jurisdictions, rationally plan site selection and scale, and clarify the final destination of sludge and specific requirements for sludge treatment and disposal. Realize the connection between medium and long-term planning and short-term risk mitigation, carry out special sludge actions, effectively dispose of existing sludge, and reduce the risk of environmental pollution.
    3) Policy support and financial guarantee for sludge resource utilization
     Based on sludge treatment and disposal projects such as environmental risk mitigation, energy resource utilization, and carbon emission reduction contribution, investment and operating costs will increase to a certain extent. The state has introduced relevant policies to subsidize its ecological value, give tax incentives to related industries, and the rational treatment and disposal of sludge will be included in the selection of ecological cities and comprehensive resource utilization cities. Local governments include sludge treatment and disposal fees from urban sewage treatment plants in their annual budgets and pay them to relevant entities in full and in a timely manner.
     From the above suggestions, it can be seen that in the future, not only sludge treatment is not only a long way to go for sewage plants, but also a work that needs supervision and financial support from relevant departments.
     Most of the sludge problems are exposed to everyone's sight, which not only shows that the sludge problem needs to be solved urgently, but also shows that sludge treatment and disposal have been put on the agenda. And with the repeated reports of environmental protection supervision, the supervision of relevant departments in various places is also increasing, if the policy funds are in place, it is believed that sludge treatment and disposal will soon open up the last mile.