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活性污泥法是目前我国处理污水最常用的方法。2020年,我国污水处理率达到了97.53%,日处理污水量超过2×108 m3,由此产生的生物污泥已突破6×107 t (以80%含水率计算) [1-2]。污泥的主要组成成分是水和有机物,有着体量大和易腐败发臭的特点。此外,污泥中还含有多种有害物质,如细菌、病毒和寄生虫卵等,若不加以处理和处置可能会危害人群健康。污泥处理和处置费用通常要占污水处理厂总费用的一半以上,主要原因是污泥高含水率导致的巨大体积问题。
在污泥最终处置前,如焚烧或填埋,需要对其进行调理脱水以达到合适的含水率 (通常60%以下) 。以聚合氯化铝 (Polyaluminum Chloride, PAC) 为调理剂的化学调理法是当下广泛使用的调理手段。与其他无机调理剂相比,PAC调理具有污泥产量少、对温度和pH不敏感等优点。针对PAC调理,相关学者进行了广泛研究。ZHAO等[3]研究了不同pH下PAC的水解过程,结果显示,随着pH的增加,单体铝和二聚铝发生聚合反应形成小的聚合铝,然后通过进一步聚合或者自组装形成中间形态的聚合铝或大的聚合铝种。CAO等[4]认为,在PAC调理过程中通过控制铝的形态来改善污泥脱水是一种新的思路。对于高级厌氧消化污泥,高碱度是其显著特征,通常碱度值高达500~8 000 mg·L−1[5]。碱度的变化不仅会影响到污泥的基本特性,也不利于PAC的水解,进而恶化调理污泥的脱水效果[6]。ZHANG等[7]研究发现,PAC水解过程中碱度变化会改变污泥的絮凝行为,在高碱度环境下,PAC水解产物的电中和及络合能力遭到削弱,调理污泥的脱水效果受到影响。在低碱度条件下,污泥颗粒与蛋白质、腐殖酸的结合增强,絮团结构更加致密,可导致污泥饼压缩性下降[8]。
污泥是一种典型的非牛顿流体,其流变学在描述污泥水力特性方面发挥重要作用,几乎影响污泥处理和处置全过程[9]。有研究发现,随着调理剂添加量的不同,污泥除了脱水性能发生改变外,也会对其流变特性产生影响[10]。在实际生产中,通过调整流变参数优化污泥管道输送可以降低运营成本[11]。但是,目前大多数研究集中于不同碱度下PAC调理污泥过程中铝形态的转化,关于流变特性变化的研究鲜有报道。本研究以热水解高级厌氧消化污泥为原料,探究了不同碱度条件下污泥理化性质的变化。并且以PAC为调理剂对不同碱度下的污泥进行调理,通过对其流变特性和脱水性能的考察,探究碱度变化对污泥脱水效果及对调理剂投加量影响,以期从污泥碱度变化的角度为污泥脱水性能的提升与调理剂的优化投加提供参考。
碱度对聚合氯化铝调理污泥脱水和流变的影响
Effect of alkalinity on dewatering and rheology of Polyaluminium Chloride conditioned sludge
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摘要: 针对厌氧消化污泥的难脱水问题,探究了不同碱度条件下污泥经聚合氯化铝调理后的脱水效果和流变特性变化。以高级厌氧消化污泥为研究对象,调节碱度后考察污泥理化性质的变化。在碱度调节的基础上投加聚合氯化铝进行调理,通过测定抽滤泥饼含固率、屈服应力和表观黏度等指标,研究不同碱度下调理污泥的脱水效果和流动性改善情况。结果表明,污泥碱度调节会对上清液中总磷和氨氮的质量浓度产生影响,可以通过碱度变化控制污泥中的P和N等元素的质量浓度。在低碱度条件下,减少聚合氯化铝的投加量可以获得较好的污泥脱水效果和流动性。当污泥碱度值为1 842.00 mg·L−1时,添加0.02 g·g−1的聚合氯化铝进行调理,抽滤泥饼的含固率达到最高值31.97%;同时,在这个条件下,污泥的极限黏度接近0,达到最低值,污泥的流动性得到了提升。调理污泥在具有最佳流动性能的同时达到最佳脱水效果。本研究结果可从污泥碱度变化的角度为污泥脱水性能的提升与调理剂的优化投加提供参考。Abstract: Aiming at the problem of difficult dehydration of anaerobic digestion sludge, the dewatering effect and rheological properties of sludge were explored, which were conditioned by polyaluminum chloride (PAC) under different alkalinity conditions. Taking advanced anaerobic digested sludge as research object, the changes of the physical and chemical properties of the sludge were investigated after adjusting the alkalinity. On the basis of alkalinity adjustment, PAC was added for conditioning. The dewatering effect and fluidity improvement of conditioned sludge under different alkalinity were researched by measuring the changes of the suction filter cake’s solid content, yield stress as well as apparent viscosity. The results demonstrated that the adjustment of the sludge alkalinity would affect the content of total phosphorus and ammonia nitrogen in the supernatant. Meanwhile, the proportion of P and N elements in the sludge could be controlled by adjusting the alkalinity. Under the condition of low alkalinity, better sludge dewatering effect and fluidity could be brought out by reducing the dosage of PAC. When the alkalinity value of the sludge was 1 842.00 mg·L−1, the conditioned sludge had a 31.97% solid content by adding PAC of 0.02 g·g−1; At the same time, the limiting viscosity of sludge was close to zero in this case, reaching the lowest value, and the fluidity of sludge was improved. Conditioned sludge had the best flow performance as well as the dehydration effect. In conclusion, the results of this study can provide some references for the improvement of sludge dewatering performance and the optimal dosing of conditioner from the perspective of sludge alkalinity adjustment.
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[1] DONG Y T, SHEN Y W, GE D D, et al. A sodium dichloroisocyanurate-based conditioning process for the improvement of sludge dewaterability and mechanism studies[J]. Journal of Environmental Management, 2021, 284: 112020-112020. doi: 10.1016/j.jenvman.2021.112020 [2] 中华人民共和国住房和城乡建设部. 2020年城市建设统计年鉴[M]. 北京: 中国统计出版社, 2020. [3] ZHAO H, LIU H J, QU J H. Effect of pH on the aluminum salts hydrolysis during coagulation process: Formation and decomposition of polymeric aluminum species[J]. Journal of Colloid and Interface Science, 2009, 330(1): 105-112. doi: 10.1016/j.jcis.2008.10.020 [4] CAO B D, ZHANG W J, WANG Q D, et al. Wastewater sludge dewaterability enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation[J]. Water Research, 2016, 105: 615-624. doi: 10.1016/j.watres.2016.09.016 [5] YANG P, LI D D, ZHANG W J, et al. Flocculation-dewatering behavior of waste activated sludge particles under chemical conditioning with inorganic polymer flocculant: Effects of typical sludge properties[J]. Chemosphere, 2019, 218: 930-940. doi: 10.1016/j.chemosphere.2018.11.169 [6] 杨鹏. 基于污泥特性的化学调理技术及其作用机制[D]. 中国地质大学, 2019. [7] ZHANG W J, TANG M Y, LI D D, et al. Effects of alkalinity on interaction between EPS and hydroxy-aluminum with different speciation in wastewater sludge conditioning with aluminum based inorganic polymer flocculant[J]. Journal of Environmental Sciences, 2021, 100: 257-268. doi: 10.1016/j.jes.2020.05.016 [8] QI Y, THAPA K B, HOADLEY A F A. Benefit of lignite as a filter aid for dewatering of digested sewage sludge demonstrated in pilot scale trials[J]. Chemical Engineering Journal, 2011, 166(2): 504-510. doi: 10.1016/j.cej.2010.11.003 [9] 曹秀芹, 柳婷, 江坤, 等. 低温热水解对污泥触变性及脱水性能的影响[J]. 环境工程学报, 2019, 13(4): 977-983. doi: 10.12030/j.cjee.201811089 [10] CHEN Q, WANG Y L. Influence of single- and dual-flocculant conditioning on the geometric morphology and internal structure of activated sludge[J]. Powder Technology, 2015, 270: 1-9. doi: 10.1016/j.powtec.2014.10.002 [11] CAO X Q, PAN Y H, JIANG K, et al. Effect of high-temperature thermal hydrolysis on rheological properties and dewaterability of sludge[J]. ENVIRONMENTAL TECHNOLOGY, 2021, 42(23): 3707-3715. doi: 10.1080/09593330.2020.1739751 [12] RAJINIKANTH R, DANIEL I. M, GURSHARAN S. A critical review on inhibition of anaerobic digestion process by excess ammonia[J]. Bioresource Technology, 2013, 143: 632-641. doi: 10.1016/j.biortech.2013.06.030 [13] 中华人民共和国国家质量监督检验检疫总局、中国国家标准化管理委员会. 城镇污水处理厂污泥处置 土地改良用泥质标准: GB/T 24600-2009[S]. 北京: 中国标准出版社, 2009. [14] MORE T T, YADAV J S S, YAN S, et al. Extracellular polymeric substances of bacteria and their potential environmental applications[J]. Journal of Environmental Management, 2014, 144: 1-25. [15] CAO B D, ZHANG T, ZHANG W J, et al. Enhanced technology based for sewage sludge deep dewatering: A critical review[J]. Water Research, 2021, 189: 116650. doi: 10.1016/j.watres.2020.116650 [16] ZHANG W J, CAO B D, WANG D S, et al. Influence of wastewater sludge treatment using combined peroxyacetic acid oxidation and inorganic coagulants re-flocculation on characteristics of extracellular polymeric substances (EPS)[J]. Water Research, 2016, 88: 728-739. doi: 10.1016/j.watres.2015.10.049 [17] 何培培, 余光辉, 邵立明, 等. 污泥中蛋白质和多糖的分布对脱水性能的影响[J]. 环境科学, 2008(12): 3457-3461. doi: 10.3321/j.issn:0250-3301.2008.12.028 [18] MURUGESAN K, RAVINDRAN B, SELVAM A, et al. Fate of extracellular polymeric substances of anaerobically digested sewage sludge during pre-dewatering conditioning with Acidithiobacillus ferrooxidans culture[J]. Bioresource Technology, 2016, 217: 173-178. doi: 10.1016/j.biortech.2016.03.081 [19] ESHTIAGHI N, MARKIS F, YAP S D, et al. Rheological characterisation of municipal sludge: A review[J]. Water Research, 2013, 47(15): 5493-5510. doi: 10.1016/j.watres.2013.07.001 [20] WEI H, GAO B Q, REN J, et al. Coagulation/flocculation in dewatering of sludge: A review[J]. Water Research, 2018, 143: 608-631. doi: 10.1016/j.watres.2018.07.029 [21] RATKOVICH N, HORN W, HELMUS F P, et al. Activated sludge rheology: A critical review on data collection and modelling[J]. Water Research, 2013, 47(2): 463-482. doi: 10.1016/j.watres.2012.11.021 [22] BIEN B, BIEN J D. Influence of digested sludge conditioning on the dewatering processes and the quality of sludge liquid[J]. Ecological Chemistry and Engineering S, 2020, 27(1): 151-164. doi: 10.2478/eces-2020-0010 [23] HII K, PARTHASARATHY R, BAROUTIAN S, et al. Rheological measurements as a tool for monitoring the performance of high pressure and high temperature treatment of sewage sludge[J]. Water Research, 2017, 114: 254-263. doi: 10.1016/j.watres.2017.02.031 [24] 曹秀芹, 王浩冉, 江坤, 等. 污泥厌氧消化过程的流变规律与脱水性能[J]. 农业工程学报, 2020, 36(5): 233-240. doi: 10.11975/j.issn.1002-6819.2020.05.027 [25] EUGENE H, ANTENEH M Y, TUSHAR K S, et al. A comprehensive review on rheological studies of sludge from various sections of municipal wastewater treatment plants for enhancement of process performance[J]. Advances in Colloid and Interface Science, 2018, 257: 19-30. doi: 10.1016/j.cis.2018.06.002