Phosphorus recovery from products of sewage sludge via different thermal treatment processes

doi:10.11949/0438-1157.20220340

Abstract

Abstract:

The experimental research on phosphorus leaching and recovery performance of sludge smoldering treatment ash was carried out, and the phosphorus leaching and recovery performance of incineration ash and pyrolysis coke produced by traditional incineration and pyrolysis treatment processes was analyzed and compared. The results showed that phosphorus content in thermal products was influenced by their residue carbon content, while phosphorus retention rate of thermal treatments was associated with their reaction violence and so on. Thermal treatment would decrease bio-availability of phosphorus in sewage sludge, especially incineration. The phosphorus leaching process of sludge smoldering ash, incineration ash and pyrolysis coke is mainly controlled by reactant concentration and product layer diffusion, and the leaching time should not exceed 8 h. Based on sulfuric acid leaching method, phosphorus leaching amount of unit mass thermal products reached 25.72—34.42 mg/g, which meant about 59.30%—84.21% of phosphorus in sewage sludge could be recovered. By further optimizing the working conditions of the leaching process, the unit consumption of sulfuric acid can be greatly reduced while maintaining a high sludge phosphorus recovery rate.

Key words: sewage sludge, waste treatment, phosphorus recovery, leaching, kinetics

摘要：

针对污泥阴燃处理灰渣开展了关于磷浸出回收性能的实验研究，并与传统焚烧和热解处理工艺所产生的焚烧灰和热解焦的磷浸出回收性能进行了分析对比。结果表明，热产物中磷含量与残碳含量有关，而热处理过程中磷留存率与反应剧烈程度等因素有关。热处理会降低污泥中磷的生物有效性，尤其是焚烧。污泥阴燃灰、焚烧灰和热解焦的磷浸出过程主要受反应物浓度和产物层扩散控制，浸出时间不应超过8 h。通过硫酸浸出污泥热处理产物的方法，单位质量热产物的磷浸出量为25.72~34.42 mg/g，可将原污泥中的磷回收59.30%~84.21%。进一步对浸出工艺进行工况优选，可在保持较高污泥磷回收率的同时大幅降低硫酸单位消耗量。

关键词: 污泥, 废物处理, 磷回收, 浸出, 动力学

CLC Number:

TK 028.8

Xinyi LUO, Chao FENG, Jing LIU, Yu QIAO. Phosphorus recovery from products of sewage sludge via different thermal treatment processes[J]. CIESC Journal, 2022, 73(9): 4034-4044.

罗欣宜, 冯超, 刘晶, 乔瑜. 污泥不同热处理工艺产物磷的浸出回收实验研究[J]. 化工学报, 2022, 73(9): 4034-4044.

Figures/Tables 13

Table 1 Proximate analysis and ultimate analysis of sewage sludge

工业分析^①/%（质量）				元素分析^②/%（质量）					高位热值/(MJ/kg)
水分^③	挥发分	灰分	固定碳	C	H	N	S	O^④	高位热值/(MJ/kg)
51.32	43.66	56.14	0.20	50.26	8.18	9.39	1.12	31.05	8.73

Fig.1 Schematic diagram of the smouldering experiment

Fig.2 Temperature profile of the combustion chamber during smouldering experiment

Fig.3 The extraction process of phosphorus speciation

Table 2 Chemical composition and carbon content of sewage sludge （SS）， smouldered ash （SA）， incinerated ash （IA） and pyrolysis char （PC）

样品	含量/%(质量)
样品	SiO₂	Al₂O₃	P₂O₅	Fe₂O₃	SO₃	CaO	K₂O	MgO	C
污泥	24.69	8.26	5.96	3.68	3.18	1.92	1.74	1.55	21.24
阴燃灰	54.73	17.56	9.44	5.85	1.94	3.46	3.15	1.68	0.60
焚烧灰	51.37	18.18	9.60	7.21	0.33	4.15	2.98	2.25	0
热解焦	49.83	18.86	8.75	6.59	1.18	4.05	3.17	2.12	13.74

Fig.4 XRD patterns of sewage sludge (SS), smouldered ash (SA), incinerated ash (IA) and pyrolyzed char (PC)

Table 3 Ash/char yield， P content and P retention rate of smouldered ash （SA）， incinerated ash （IA） and pyrolysis char （PC）

样品	Y/ (g/g)	P/ (mg P/g)	R/%
阴燃灰	0.58	41.22	92.50
焚烧灰	0.54	41.93	87.02
热解焦	0.66	38.20	96.89

Fig.5 P mineral species distribution and Bio-P in sewage sludge (SS), smouldered ash (SA), incinerated ash (IA) and pyrolysis char (PC)

Fig.6 Phosphorus leaching proportion of smouldered ash (SA), incineration ash (IA) and pyrolysis char (PC) under different H2SO4 concentrations and liquid/solid ratios

Table 4 R2and K of the kinetic models

动力学模型		阴燃灰		焚烧灰		热解焦
动力学模型		R²	K/s^-1	R²	K/s^-1	R²	K/s^-1
Ⅰ	$1 - {(1 - α)}^{1 / 3} = k_{1} t$	0.9587	0.0086	0.9100	0.0296	0.9120	0.0077
Ⅱ	$1 - \frac{2}{3} α - {(1 - α)}^{2 / 3} = k_{2} t$	0.9706	0.0030	0.9195	0.0125	0.9177	0.0036
Ⅲ	${(1 - α)}^{- 1 / 3} - 1 + \frac{1}{3} l n (1 - α) = k_{3} t$	0.9812	0.0033	0.9415	0.0192	0.9393	0.0073
Ⅳ	$0.2 {(1 - α)}^{- 5 / 3} - 0.25 {(1 - α)}^{- 4 / 3} + 0.05 = k_{4} t$	0.9893	0.0095	0.9655	0.0875	0.9616	0.0474

Table 4 R2and K of the kinetic models

动力学模型		阴燃灰		焚烧灰		热解焦
动力学模型		R²	K/s^-1	R²	K/s^-1	R²	K/s^-1
Ⅰ	$1 - {(1 - α)}^{1 / 3} = k_{1} t$	0.9587	0.0086	0.9100	0.0296	0.9120	0.0077
Ⅱ	$1 - \frac{2}{3} α - {(1 - α)}^{2 / 3} = k_{2} t$	0.9706	0.0030	0.9195	0.0125	0.9177	0.0036
Ⅲ	${(1 - α)}^{- 1 / 3} - 1 + \frac{1}{3} l n (1 - α) = k_{3} t$	0.9812	0.0033	0.9415	0.0192	0.9393	0.0073
Ⅳ	$0.2 {(1 - α)}^{- 5 / 3} - 0.25 {(1 - α)}^{- 4 / 3} + 0.05 = k_{4} t$	0.9893	0.0095	0.9655	0.0875	0.9616	0.0474

Fig.7 Kinetic simulation of phosphorus leaching from smouldered ash (SA), incineration ash (IA) and pyrolysis char (PC)

Table 5 P recovery capability and leaching agent consumption of smouldered ash （SA）， incinerated ash （IA） and pyrolysis char （PC）

样品	最高磷浸出工况			优选工况
样品	磷回收率^①/%（质量）	磷浸出量/(mg P/g)	硫酸单位消耗量/mmol	磷回收率^①/%（质量）	磷浸出量/(mg P/g)	硫酸单位消耗量/mmol
阴燃灰	59.30	25.72	0.16	56.58	24.54	0.082
焚烧灰	70.10	34.42	0.15	67.59	33.19	0.060
热解焦	84.21	33.71	0.30	62.96	25.20	0.079

Fig.8 H2SO4 unit consumption of smouldered ash (SA), incineration ash (IA) and pyrolysis char (PC) under leaching conditions

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