【作者】 张莹；

【导师】 王小铭；

【作者基本信息】 重庆大学 ， 环境科学与工程， 2022， 硕士

【摘要】 近年来,随着我国城镇化的发展以及对环境质量要求的不断提高,我国污水处理量急剧增加,作为污水处理主要副产物之一的污泥,其产量也迅速上升。传统的污泥填埋或水泥窑协同处理等方式已逐渐不能满足需求,因此如何高效处置污水污泥成为研究热点。水热炭化(HTC)技术具有不受原料含水率限制、将湿废弃物转化为可资源化利用材料的优点,因此,HTC被认为是一种极具潜力的污泥处理方式。然而,现有研究表明,我国污水污泥的灰分含量较高,限制了HTC处理产物的资源化利用潜力。因此,本研究提出将污水污泥与低灰分含量的生物质废弃物进行共水热炭化(Co-HTC)处理,并研究处理后产物的理化性质,以期为污泥问题的解决提供科学依据。本研究主要研究内容及结论包括以下几个方面:(1)共水热产物理化性质分析。以污水污泥为原料,以湿地植物、玉米秸秆、蔬菜废弃物为添加物,在220℃下Co-HTC处理2 h。通过测定固、液、气三相产物的产率,研究其分配特征;通过对三相产物理化性质表征,分析产物的基本性质。研究发现原料干物质经Co-HTC处理后,产物主要分布在固相(40～64%)和液相(25～45%)中,仅有少部分转移到气相中(8～14%)。水热炭性质:扫描电镜图表明随着添加物比例的增加,水热炭表面逐渐出现较为清晰的炭微球和孔隙。相比于试验原料,水热炭中碳元素含量增加,水热处理可以促进碳元素的富集。炭化液性质:p H值和电导率值分别为4.00～7.40和1.15～4.70 ms/cm,添加物的存在可以降低炭化液的p H值和电导率值。COD、总氮、氨氮、硝态氮和总磷的范围分别为26375～53096、843.5～1725.9、308.0～540.6、18.6～328.5和9.5～47.5 mg/L。气相产物性质:产物均检测到了一氧化碳、二氧化碳、甲烷、氢气和氮气,其中二氧化碳含量最高(59.6～73.4%)。此外,硫化氢含量也较高(1020～2321 ppm)。(2)水热炭燃料化与肥料化利用潜力研究。通过水热炭的燃烧性能和燃烧行为分析,从理论上阐述水热炭燃料化利用的可行性,并与国家标准《商品煤质量发电煤粉锅炉用煤》(GB/T 7562-2018)中的指标进行对比,从应用层面上分析水热炭燃料化利用潜力。为评估水热炭肥料化利用前景,参考《绿化用有机基质》(GB/T33891-2017)标准中的技术、安全指标进行评估。对于燃料利用潜力:理论分析表明水热炭的热值范围为8.0～22.3 MJ/kg;与所有原料相比,水热炭的H/C和O/C原子比显著降低,且着火温度更高,这表明水热炭用作燃料的品质提升。应用分析表明水热炭的挥发分含量满足发电煤粉锅炉用褐煤的要求(污泥单独HTC处理衍生水热炭除外);水热炭灰分含量较高,几乎均未达到国家标准要求;磷、氯和汞含量均超出了国家标准限值,砷含量在国家标准范围内。对于肥料利用潜力:水热炭的p H值(5.16～6.36)、电导率值(1.53～3.00 ms/cm,蔬菜废弃物单独HTC处理除外)总养分(6.32～23.36%)、水解性氮(≤3000 mg/kg,污泥单独HTC处理除外)、速效钾(1316～3953 mg/kg)、发芽指数(92～148%)、可溶性钠(147～925 mg/L,蔬菜废弃物单独HTC处理除外)、有机质(42.70～78.07%,污泥单独HTC处理除外)和大部分组次的重金属含量满足标准中的技术、安全指标要求。但有效磷含量较高(325～3202 mg/kg),基本上不满足指标要求,但未来可考虑将水热炭制成补磷有机肥。87%的水热炭可溶性氯含量超出标准。由此可见,水热炭具有用作燃料和肥料的潜力,但部分指标或部分组次的指标超标,在水热炭实际应用前须采取措施进行调控。(3)炭化液用作补充碳源的可行性研究。通过理论分析和反硝化模拟试验测定,研究炭化液用作污水处理厂补充碳源的可行性。理论分析表明将炭化液与污水处理厂的缺氧池污水混合后,池内COD、总氮、总磷浓度可分别提高12.9～26.1、1.0～2.2、2.0～10.1%。同时,污泥单独HTC后,将炭化液投加至缺氧池(原C/N比为2.6)中,池中污水的C/N比为3.0,提升程度为16.8%;假设污水污泥:添加物=1:1时,炭化液投加后,池中污水的C/N比为3.6～3.7,提升程度达36.6～43.1%。反硝化模拟试验表明炭化液的投加对硝态氮去除有正向促进作用,添加了炭化液的试验组硝态氮去除率均>93%(空白组71%)。因此炭化液具有用作低碳氮比废水补充碳源的潜力,且添加物的存在提升了这一潜力。(4)共水热处理能量衡算。通过计算Co-HTC处理污泥过程中的输入能量与输出能量,并将两者进行对比,分析该过程的能量平衡,评估能量转化效率。结果发现,污泥单独HTC处理时,结余能量为700.9 KJ(2 kg反应原料),其余Co-HTC处理后的能量结余为1210.9～1919.5 KJ(2 kg,不考虑添加物单独HTC处理组次)。由此可见,Co-HTC处理有利于能量的回收利用,添加物可以显著提升回收的能量值。更多还原

【Abstract】 In recent years,with the development of urbanization and the improvement of environmental quality,the amount of sewage treatment in our country has increased sharply.As one of the main by-products of sewage treatment,the output of sludge has also increased rapidly.Traditional sludge treatment such as landfill or cement kiln coprocessing methods can not meet the demand gradually.Therefore,how to effectively treat sewage sludge has become the focus of many researchers.Hydrothermal carbonization(HTC)technology has the advantage of converting wet wastes into recyclable materials without the limitation of water content of raw materials.Therefore,HTC is considered to be a very promising sludge treatment method.HTC treatment of sludge is considered to be a solution with great potential for sludge treatment.However,existing studies have shown that the ash content of sewage sludge is high,which will limit the resource utilization potential of products.Therefore,this study proposed to treat sewage sludge with biomass waste with low ash content by co-hydrothermal carbonization(Co-HTC).and studies the physical and chemical properties of the treated products,in order to provide a scientific basis for the solution of sludge problems.The specific work done and the main conclusions of this study include the following aspects:(1)Analysis of physical and chemical properties of Co-HTC production.Sewage sludge was used as raw material,and wetland plants,corn stalks or vegetable waste were used as additives,and Co-HTC was carried out at 220 ℃ for 2 h.By measuring the yields of solid,liquid and gas three-phase products,the distribution characteristics of the three-phase products were studied;the basic properties of the products were analyzed by characterizing the physical and chemical properties of the three-phase products.It is found that the dry matter of raw material is mainly distributed in solid phase(40～64%)and liquid phase(25～45%)after Co-HTC treatment,and only a small part of the dry matter is transferred to gas phase(8～14%).Properties of hydrochar: SEM images showed that with the increase of the proportion of additives,relatively clear carbon microspheres and pores gradually appeared on the surface of hydrochar.Compared with the experimental raw materials,the carbon content in the hydrochar increases,and the HTC treatment can promote the enrichment of carbon.Properties of carbonization liquid: p H and conductivity values are 4.00～7.40 and 1.15～4.70 ms/cm,respectively.The presence of additives can reduce the p H and conductivity of carbonization liquid.The ranges of COD,total nitrogen,ammonia nitrogen,nitrate nitrogen and total phosphorus were26375～53096,843.5～1725.9,308.0～540.6,18.6～328.5 and 9.5～47.5 mg/L,respectively.Properties of gas phase products: Carbon monoxide,carbon dioxide,methane,hydrogen and nitrogen were detected in all products,with the highest content of carbon dioxide(59.6～73.4%).In addition,the hydrogen sulfide content is also high(1020～2321 ppm).(2)Research on the potential of hydrochar fuel and fertilizer utilization.By analyzing of the combustion performance and combustion behavior of hydrochar,the feasibility of hydrochar fuel utilization is expounded in theory.Compared with the indicators in the national standard "Commercial Coal Quality for Power Generation Pulverized Coal Boiler"(GB/T 7562-2018),and the application potential of hydrochar fuel is analyzed.In order to evaluate the utilization prospect of hydrochar as fertilizer,the technical and safety indicators in "Organic Substrate for Greening"(GB/T 33891-2017)shall be referred to.For fuel utilization potential: theoretical analysis shows that the higher heating values of hydrochar ranges from 8.0 to 22.3 MJ/kg.Compared with all raw materials,the H/C and O/C atomic ratios of hydrochar are significantly lower,and the ignition temperature is higher,which indicates the improved quality of hydrochar used as fuel.Application analysis showed that the volatile content of hydrochar meets the requirements of lignite used in pulverized coal boilers for power generation(except for hydrochar derived from HTC treatment of sludge alone).The content of chlorine and mercury exceeded the national standard limit,and the arsenic content was within the national standard.For fertilizer utilization potential: the p H value(5.16～6.36),conductivity value(1.53～3.00 ms/cm,except group vegetable waste separate HTC treatment),total nutrients(6.32～23.36%),hydrolyzable nitrogen(≤3000 mg/ kg,except group sludge separate HTC treatment),available potassium(1316～3953 mg/kg),germination index(92～148%),soluble sodium(147～925 mg/L,except group vegetable waste separate HTC treatment),organic matter(42.70～78.07%,except groups sludge separate HTC treatment)and the heavy metal content of most groups meet the technical and safety index requirements in the standard.However,the available phosphorus content is high(325～3202 mg/kg),which basically does not meet the index requirements,but in the future,hydrochar can be considered as phosphorus-supplementing organic fertilizer.87% of hydrochar soluble chlorine content exceeds the standard.It can be seen that hydrochar has the potential to be used as fuel and fertilizer,but some indicators or some groups of indicators exceed the standard,and measures must be taken to regulate before the practical application of hydrothermal charcoal.(3)Feasibility study of carbonization liquid as supplementary carbon source.Through theoretical analysis and denitrification simulation test,the feasibility of carbonization liquid used as supplementary carbon source in sewage treatment plant is studied.Theoretical analysis shows that the COD,total nitrogen and total phosphorus concentrations can be increased by 12.9～26.1,1.0～2.2,2.0～10.1% respectively after mixing the carbonization liquid with the anoxic wastewater of the wastewater treatment plant.At the same time,after the sludge is HTC alone,the carbonization liquid is added to the anoxic tank(the original C/N ratio is 2.6),the C/N ratio of the sewage in the tank is 3.0,and the degree of improvement is 16.8%.Assuming that the sewage sludge:additive = 1:1,after the carbonization liquid is added,the C/N ratio of the sewage in the pool is 3.6～3.7,and the improvement degree is 36.6～43.1%.The denitrification simulation test shows that the addition of carbonization liquid has a positive effect on the removal of nitrate nitrogen.Therefore,the carbonization liquid has the potential to be used as a supplementary carbon source for low carbon nitrogen ratio wastewater,and the presence of additives enhances this potential.(4)Co-hydrothermal treatment energy balance.By calculating the input energy and output energy of Co-HTC sludge treatment process,and analyzing the energy balance of the process,the energy conversion efficiency was evaluated.The results showed that the residual energy was 700.9 KJ(2kg reaction raw material)when only sludge was treated by HTC(Groups 1,6,11),and the residual energy after treatment by Co-HTC was1210.9～1919.5 KJ(2kg,without considering the separate HTC treatment test group of additives).It can be seen that the Co-HTC treatment is beneficial to the recovery and utilization of energy,and the additive can significantly improve the recovered energy value.更多还原