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近年来,提高大中型城镇污水处理厂废水处理过程能源利用率,降低污水处理厂碳排放量成为研究热点[1]。城镇污水处理厂消耗能源有电能、药剂和燃料等,电能占总能耗的60%~90%,曝气池消耗电能占总运行电耗的51.81%[2],其中,部分电耗被用于难降解有机物的去除,造成了资源的浪费。因此,有必要更新污水处理工艺,改变污水处理厂运行思路,以减少能源消耗和提高能源回收率,提高污水处理厂效益。
生物絮凝工艺具有微生物浓度高、污泥龄短、有机负荷高等特点,可有效利用微生物分泌的胞外聚合物(EPS)截留进水所含颗粒态和胶体态有机物、悬浮态无机物、重金属等物质[3-4]。活性污泥絮体中EPS作为微生物主要成分之一[5],除具有形成和保护活性污泥絮体结构功能外,还有良好的絮凝功能[6]。但是由于EPS提取工艺不成熟、组成成分不尽相同、各组分功能尚不明确等原因使其无法被广泛应用[7-8]。生物絮凝系统不仅可以发挥EPS絮凝颗粒态和难降解有机物的能力,还可减少化学药剂使用量,进而降低污水处理成本,减轻污水处理厂对环境的负面影响。
生物絮凝系统通过截留难降解有机物,可降低二级处理过程中的电能消耗,从而减少温室气体的间接排放。此外,生物絮凝系统内微生物与有机物絮凝后产生有机质含量较高的剩余污泥,可用于厌氧发酵产酸,相应挥发性脂肪酸平均浓度可达7.93 g·L−1[9]。因此,有机酸可作为优质碳源,投加至厌氧池或缺氧池内,以强化污水处理厂脱氮除磷效果,减少除磷药剂和外加碳源的使用量,从而进一步降低污水处理厂污水处理成本与温室气体排放量。
本研究以城镇污水为对象,在中试规模下研究了生物絮凝系统对实际污水中污染物的去除效果与污泥产量变化影响,考察了不同水力停留时间下生物絮凝系统内EPS合成规律,并核算了生物絮凝系统温室气体排放量,为污水处理厂节能降耗与资源回收利用提供参考。
低碳排放的生物絮凝中试系统污染物去除特性及污泥EPS变化
Pollutant removal characteristics and sludge EPS changes of bioflocculation pilot system with low carbon emission
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摘要: 用中试规模生物絮凝工艺处理含化学絮凝剂的生活污水,分别研究了HRT和进水SS对生物絮凝系统污染物去除特性、剩余污泥产量、污泥特性和温室气体排放的影响。结果表明:生物絮凝系统对COD、TN和TP有较好的去除效果,且污染物去除效果受进水SS影响较大;生物絮凝系统平均污泥产量和平均有机物产量最高可达 53.63 kg·d−1和21.14 kg·d−1;污泥胞外聚合物EPS浓度和PN/PS均与有机负荷呈反比;化学絮凝剂通过影响PN/PS和EPS浓度,可间接影响污泥的沉降性能;生物絮凝系统与AAO工艺相结合,可降低50.12 g·m−3温室气体的排放。因此,生物絮凝工艺可为污水处理厂节能降耗运行奠定基础,有望得到广泛应用。Abstract: The pilot-scale bioflocculation process was used to treat domestic wastewater containing chemical flocculants. The performance of the bioflocculation system in terms of contaminants removal, excess sludge production, sludge characteristics and carbon emission reduction were investigated under variations of hydraulic retention time (HRT) and the influent suspended solids (SS). The experimental results showed that the bioflocculation system had a good removal effect on insoluble chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and the pollutant removal effect was greatly affected by the influent SS. The average sludge yield and predicted average organic matter production (in terms of acetic acid) were up to 53.63 kg MLSS·d−1 and 7.08 kg·d−1, respectively. Both the extracellular polymeric substances (EPS) content and PN/PS were negatively correlated with the organic loading rate. In addition, the chemical flocculant had an indirect effect on the settling property of bioflocculation sludge through influencing the EPS content and PN/PS. The combination of bioflocculation process and AAO process could reduce 50.12 g·m−3 carbon dioxide (CO2) emission. Moreover, greenhouse gas emission could decrease along with the anaerobic fermentation process through acid production. Therefore, the bioflocculation process can lay a foundation for the energy saving and consumption reduction operation in wastewater treatment plants, will be widely used in practice.
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表 1 中试系统进水水质
Table 1. Influent quality of pilot-scale system
mg·L−1 浓度与平均值 COD TN ${\rm{NH}}_4^{+} $ -NTP SS Al Fe 浓度 245~852 34.46~54.99 26.95~41.31 6~32 400~2 400 2~10 2~8 平均值 417.50±177.89 44.17±6.20 33.48±4.03 14.04±6.96 1 362.50±740.54 5±0.12 3±0.15 表 2 生物絮凝系统运行参数
Table 2. Operational parameters of bioflocculation system
运行阶段 时间/d 流量/(m3·h−1) HRT/h SS/(mg·L−1) 1 1~11 1.25 0.80 1 500~2 400 2 12~22 2.10 0.50 1 500~2 400 3 23~33 3.30 0.30 1 500~2 400 4 34~53 2.10 0.50 400~700 表 3 每吨水温室气体排放量对比(以CO2计算)
Table 3. Comparison of greenhouse gas emissions per ton of wastewater (calculated in carbon dioxide)
g·m−3 中试系统及处理厂 污水处理过程CH4的排放量 污水处理过程N2O的排放量 用电造成的温室气体排放 温室气体总排放量 生物絮凝中试系统 0 0 28.78 28.78 某污水处理厂 150.38 0.22 372.56 523.16 -
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