Transformation of Fe3+ and its effect on anoxic sludge flocculation in A2O process

doi:10.11949/j.issn.0438-1157.20180793

Abstract

Abstract:

To study the effect of iron on the flocculation of A²O process sludge, the distribution and migration and tranformation of Fe³⁺ in sludge supernatant, extracellular polymeric substances (EPS) and sediment (Pellet) were investigated. A large amount of wastewater containing Fe³⁺ was generated in the rapidly developed industries such as metallurgy, electroplate and mineral separation. Fe³⁺ entered the sewage biological treatment system and could affect the sludge biological flocculation and the removal of COD, TN and TP. Information on the morphology, structure change, migration and conversion of iron ions in the anaerobic, anoxic and oxic sludge was scrace. The occurrence form and structural characteristics of iron ions were analyzed and the interaction mechanism between Fe³⁺ and microbial metabolites was revealed based on the analyses of three-dimensional excitation (3D-EEM), atom absorption and X-ray diffraction (XRD). The effect of Fe³⁺ on the denitrification and phosphorus removal was explored. The results showed that low concentration of Fe³⁺(<10 mg·L^-1) could improve COD and TN removal, promote microbial activity and enhance the biological flocculation of sludge. When Fe³⁺ increased from 0 to 10 mg·L^-1, the removal efficiency of COD and TN increased from 42% and 37% to 60% and 45%, respectively, while the dehydrogenase activity increased from 20.09 mg·(L·h)^-1 to 31.91 mg·(L·h)^-1. The flocculation ability (FA) increased from 30% to 53% and the maximum sludge particle size was 43.3 μm. High concentration of Fe³⁺ could inhibit microbial activity, increase EPS content and induce sludge deflocculation. When Fe³⁺ concentration increased from 10 mg·L^-1 to 40 mg·L^-1, the removal efficiency of COD and TN decreased by 28% and 34%, respectively. Protein (PN)/polysaccharide (PS) in loosely bound EPS(LB) and tightly bound EPS(TB) was the key factor affecting the flocculation of sludge. Fe³⁺ addition could enhance TP removal efficiency and it was 93% when Fe³⁺ was 40 mg·L^-1. Fe³⁺ concentration distribution in the sludge was TB>supernatant>LB>soluble microbial products(SMP), and the main form of Fe element in the sludge was Fe³⁺. The iron content of different forms changed with the increase of Fe³⁺ concentration. In addition, Fe³⁺ could enrich and accumulate in the microorganism cells and could change the composition of EPS layers.

Key words: iron, wastewater, bioreactors, anoxic sludge, migration and transformation, morphology, biological flocculation

摘要：

为了研究铁元素对A²O工艺污泥絮凝性的影响，考察Fe³⁺在污泥上清液、胞外聚合物（extracellular polymeric substances，EPS）与底泥（Pellet）中的分布和迁移转化规律，结合三维荧光光谱（3D-EEM）、原子吸收和X射线衍射仪（XRD）分析Fe的存在形态和结构特征，揭示Fe³⁺与微生物代谢产物的作用机制，探索Fe³⁺对脱氮除磷效率的影响。结果表明：低浓度Fe³⁺（<10 mg·L^-1）能够提高COD和TN去除率，促进微生物活性，增强污泥生物絮凝性；高浓度Fe³⁺（10~40 mg·L^-1）则抑制微生物活性，使EPS总量升高，污泥絮体脱稳，LB、TB层PN/PS是影响污泥絮凝性的关键因素；Fe³⁺的投加强化生物除磷效率，当Fe³⁺浓度为40 mg·L^-1时，TP去除率为93%。Fe³⁺在污泥混合液中的分布规律为TB>上清液>LB>SMP，Fe³⁺在生物体内富集累积，能够改变EPS各层的组分。

关键词: Fe, 废水, 生物反应器, 缺氧污泥, 迁移转化, 形态学, 生物絮凝性

CLC Number:

X 703

Lanhe ZHANG, Mingshuang ZHANG, Jingbo GUO, Yanping JIA, Zheng LI, Zicheng CHEN. Transformation of Fe³⁺ and its effect on anoxic sludge flocculation in A²O process[J]. CIESC Journal, 2019, 70(3): 1089-1098.

张兰河, 张明爽, 郭静波, 贾艳萍, 李正, 陈子成. Fe³⁺在A²O工艺缺氧区的转化规律及其对污泥絮凝性的影响[J]. 化工学报, 2019, 70(3): 1089-1098.

Figures/Tables 12

Fig.1 Schematic diagram of A2O process

Table 1 Index of influent wasterwater

COD/(mg·L^-1)	TN/(mg·L^-1)	$N H 4 +$ -N/(mg·L^-1)	TP/(mg·L^-1)	$P O 4 3 -$ -P/(mg·L^-1)	DO/(mg·L^-1)	pH	T/℃
480—500	68—71	52—56	7.5—8.0	7.0—7.6	0.1—0.12	7.4—7.8	19—25

Table 1 Index of influent wasterwater

COD/(mg·L^-1)	TN/(mg·L^-1)	$N H 4 +$ -N/(mg·L^-1)	TP/(mg·L^-1)	$P O 4 3 -$ -P/(mg·L^-1)	DO/(mg·L^-1)	pH	T/℃
480—500	68—71	52—56	7.5—8.0	7.0—7.6	0.1—0.12	7.4—7.8	19—25

Fig.2 Extraction flow chart of EPS

Fig.3 Extraction flow chart of different forms of iron

Fig.4 Effect of Fe3+ on removal efficiency of COD, TN and TP in anoxic zone

Fig.5 Effect of Fe3+ on dehydrogenase content in anoxic zone

Fig.6 Distributions of Fe in sludge mixture in anoxic zone

Fig.7 Three-dimensional fluorescence spectra of EPS under different concentrations of Fe3+

Fig.8 Change of iron content in different forms of Pellet

Fig.9 XRD patterns of different concentrations of Fe3+

Fig.10 Effect of Fe3+ on flocculation in anoxic zone

Table 2 Effect of Fe3+ on EPS， PN and PS contents

Fe³⁺/ (mg·L^-1)	PN/(mg·L^-1)			PS/(mg·L^-1)			PN/PS			EPS/(mg·L^-1)
Fe³⁺/ (mg·L^-1)	SMP	LB	TB	SMP	LB	TB	SMP	LB	TB	SMP	LB	TB
0	5.17	11.83	38.5	5.66	2.86	6.42	0.9	4.14	6.00	10.83	14.69	44.92
5	15.17	21.83	55.17	5.47	5.09	6.98	2.77	4.29	7.90	20.64	26.93	64.15
10	21.83	18.5	96.83	4.91	3.58	7.55	4.45	5.16	12.83	26.76	22.08	104.38
20	40.17	16.83	108.5	6.6	5.47	9.06	6.08	3.08	11.98	46.27	22.30	117.56
30	38.5	21.83	96.83	6.79	6.6	16.04	5.67	3.31	6.04	45.29	28.44	112.87
40	51.83	31.83	118.5	8.49	7.36	18.68	6.10	4.33	6.34	60.32	39.19	137.18

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Transformation of Fe³⁺ and its effect on anoxic sludge flocculation in A²O process

Fe³⁺在A²O工艺缺氧区的转化规律及其对污泥絮凝性的影响

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