Temporal changes of heavy metals in sludge under the condition of straw charcoal assisted earthworm composting
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摘要:
为降低生活污泥中重金属迁移性和有效性,提高其利用率,以某市生活污水处理厂剩余污泥为研究对象,设置污泥单独堆肥为对照组,添加蚯蚓和不同比例玉米秸秆炭(0%、2%、4%、6%和8%),探究秸秆炭协助蚯蚓堆肥条件下污泥中重金属浓度及其有效态的时间变化规律。结果表明,随堆肥时间增加(0~30 d),污泥pH和总氮(TN)浓度先升高后降低,总有机碳(TOC)浓度逐渐降低,电导率(EC)先降低后升高,总磷(TP)和总钾(TK)浓度逐渐增加,堆肥结束时,pH、TOC浓度和TN浓度分别较初始值平均降低6.38%、20.24%和13.44%;重金属Cd、Zn和Pb浓度先降低后升高,Cu、Ni和Cr浓度先升高后降低;重金属Cd、Cu、Ni和Zn有效态浓度先降低后升高,Cr和Pb有效态浓度先升高后降低,堆肥10 d时,Cd、Cu、Ni和Zn有效态浓度较初始值降低最多,平均降低40.99%、30.65%、16.23%和3.17%。秸秆炭的添加能改善污泥弱酸性环境,提高TK浓度,降低EC和TOC、TN、TP浓度;污泥中重金属(除Pb外)浓度及其有效态(除Cu和Pb外)浓度均随秸秆炭添加比例的增加而降低。通过相关性和逐步回归分析得出,秸秆炭协助蚯蚓堆肥主要通过改变污泥pH及EC与TOC、TP浓度影响重金属有效态浓度,且添加8%玉米秸秆炭时污泥中重金属浓度和有效态浓度降低效果最佳。
Abstract:In order to reduce the migration and availability of heavy metals in domestic sludge and improve its utilization rate, the residual sludge of a municipal domestic sewage treatment plant was taken as the research object, the sludge by composting alone was set as the control group, and the earthworms and different proportions of corn straw charcoal (0%, 2%, 4%, 6% and 8%) were added, to study the time variation of heavy metal concentrations and their effective state in sludge under the condition of straw charcoal assisted earthworm composting. The results showed that with the increase of composting time (0-30 d), the pH and TN concentrations of sludge first increased and then decreased, the TOC concentration gradually decreased, the EC concentration first decreased and then increased, and the TP and TK concentrations gradually increased. At the end of composting, the pH, TOC and TN concentrations decreased by 6.38%, 20.24% and 13.44% on average compared with the initial values, respectively. The concentrations of heavy metals Cd, Zn and Pb decreased first and then increased, while the concentrations of Cu, Ni and Cr increased first and then decreased. The effective concentrations of heavy metals Cd, Cu, Ni and Zn decreased first and then increased, and the effective concentrations of Cr and Pb increased first and then decreased. After 10 days of composting, the effective concentrations of Cd, Cu, Ni and Zn decreased the most compared with the initial values, with an average decrease of 40.99%, 30.65%, 16.23% and 3.17%, respectively. The addition of straw carbon could improve the weak acid environment of sludge, increase the concentration of TK, and decrease the concentrations of EC, TOC, TN and TP. The concentrations of heavy metals in sludge (except Pb) and their effective state concentrations (except Cu and Pb) decreased with the increase of the proportion of carbon added to straw. Through correlation and stepwise regression analysis, it was concluded that straw charcoal assisted earthworm composting mainly affected the effective concentration of heavy metals by changing the sludge pH and the concentrations of EC, TOC and TP, and the addition of 8% corn straw charcoal had the best effect on reducing the concentrations and effective concentrations of heavy metals in the sludge.
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Key words:
- urban domestic sludge /
- earthworm compost /
- corn straw charcoal /
- heavy metal
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表 1 物料的基本理化性质
Table 1. Basic physiochemical properties of raw materials
指标 污泥 秸秆炭 pH 6.65±0.02 8.87±0.09 电导率(EC)/(mS/cm) 3.55±0.09 0.86±0.05 总有机碳(TOC)浓度/% 40.41±3.59 23.78±0.63 总氮(TN)浓度/(g/kg) 22.71±0.06 0.63±0.05 总磷(TP)浓度/(g/kg) 5.88±0.30 2.82±0.10 总钾(TK)浓度/(g/kg) 0.27±0.01 15.90±0.70 Cd浓度/(mg/kg) 3.14±0.01 0.05±0.00 Cu浓度/(mg/kg) 76.55±4.23 19.37±0.66 Ni浓度/(mg/kg) 55.12±1.49 2.45±0.07 Zn浓度/(mg/kg) 109.43±0.15 — Cr浓度/(mg/kg) 216.79±22.96 — Pb浓度/(mg/kg) 41.83±6.24 — 注:—表示未检出。全文同。 表 2 污泥标准中重金属浓度限值
Table 2. Limit values of heavy metal contents in sewage sludge standards
mg/kg 标准 Cd Cu Ni Zn Cr Pb 中国 GB 4284—
2018 A级<3 <500 <100 <1 200 <500 <300 GB 4284—
2018 B级<15 <1 500 <200 <3 000 <1 000 <1 000 欧盟 20~40 1 000~
1 750300~
4002 500~
4 000750~
1 200日本 <150 <250 <150 美国 <39 <1500 <420 <2 800 <300 表 3 重金属有效态浓度与堆肥污泥理化性质的相关性
Table 3. Correlation between the effectiveness of heavy metals and the physicochemical properties of compost sludge
参数 Cd Cu Ni Zn Cr Pb pH −0.656** −0.802** −0.580** −0.412** 0.473** 0.116 EC 0.705** 0.792** 0.547** 0.321* −0.579** −0.136 TOC −0.397** −0.692** −0.200 0.059 0.596** 0.071 TN −0.086 −0.445** −0.237 −0.254 0.064 0.076 TP 0.505** 0.693** 0.275 −0.032 −0.639** −0.257 TK 0.143 0.290* 0.073 0.029 −0.203 −0.185 注:*表示在P<0.05下相关性显著,**表示在P<0.01下相关性显著。 表 4 重金属有效态浓度与理化性质的回归方程
Table 4. Regression equation between the availability of heavy metals with physical and chemical properties of sludge
重金属 逐步回归方程 R2 P 标准估算
的误差浓度
预测值/(mg/kg)Cd y=0.013XEC+0.064 0.486 <0.01 0.035 0.076~0.185 Cu y=−9.229XpH−
0.569XTOC+94.3210.759 <0.01 3.030 0.000~19.383 Ni y=−1.013XpH+12.226 0.322 <0.01 0.589 4.679~5.945 Zn y=−0.564XpH−
0.028XTP+27.3460.238 <0.05 0.321 22.508~23.816 Cr y=−0.086XTP+1.546 0.395 <0.01 0.529 0.000~1.445 Pb -
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