Energy neutrality potential of wastewater treatment plants: A novel evaluation framework integrating energy efficiency and recovery

doi:10.1007/s11783-022-1549-0

Front. Environ. Sci. Eng.

2022, Vol. 16

Issue (9) : 117 https://doi.org/10.1007/s11783-022-1549-0

RESEARCH ARTICLE

Energy neutrality potential of wastewater treatment plants: A novel evaluation framework integrating energy efficiency and recovery

Runyao Huang^1,², Jin Xu¹, Li Xie^1,³, Hongtao Wang^1,^2,³(

), Xiaohang Ni¹

¹. Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
². UNEP-Tongji Institute of Environment for Sustainable Development, Tongji University, Shanghai 200092, China
³. Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China

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Abstract

• Framework of indicators was established based on energy efficiency and recovery.

• Energy neutrality potential of 970 wastewater treatment plants was evaluated.

• Analysis of characteristics and explanatory factors was carried out.

• Pathways for improving the energy neutrality potential were proposed.

Wastewater treatment plants (WWTPs) consume large amounts of energy and emit greenhouse gases to remove pollutants. This study proposes a framework for evaluating the energy neutrality potential (ENP) of WWTPs from an integrated perspective. Operational data of 970 WWTPs in the Yangtze River Economic Belt (YREB) were extracted from the China Urban Drainage Yearbook 2018. The potential chemical and thermal energies were estimated using combined heat and power (CHP) and water source heat pump, respectively. Two key performance indicators (KPIs) were then established: the energy self-sufficiency (ESS) indicator, which reflects the offset degree of energy recovery, and the comprehensive water–energy efficiency (CWEE) indicator, which characterizes the efficiency of water–energy conversion. For the qualitative results, 98 WWTPs became the benchmark (i.e., CWEE= 1.000), while 112 WWTPs were fully self-sufficient (i.e., ESS≥100%). Subsequently, four types of ENP were classified by setting the median values of the two KPIs as the critical value. The WWTPs with high ENP had high net thermal energy values and relatively loose discharge limits. The explanatory factor analysis of water quantity and quality verified the existence of scale economies. Sufficient carbon source and biodegradability condition were also significant factors. As the CWEE indicator was mostly sensitive to the input of CHP, future optimization shall focus on the moisture and organic content of sludge. This study proposes a novel framework for evaluating the ENP of WWTPs. The results can provide guidance for optimizing the energy efficiency and recovery of WWTPs.

Keywords Wastewater treatment plants Energy neutrality potential Energy efficiency Energy recovery Evaluation framework

Corresponding Author(s): Hongtao Wang

About author:

Tongcan Cui and Yizhe Hou contributed equally to this work.

Issue Date: 14 February 2022

Cite this article:

Runyao Huang,Jin Xu,Li Xie, et al. Energy neutrality potential of wastewater treatment plants: A novel evaluation framework integrating energy efficiency and recovery[J]. Front. Environ. Sci. Eng., 2022, 16(9): 117.

URL:

https://academic.hep.com.cn/fese/EN/10.1007/s11783-022-1549-0
https://academic.hep.com.cn/fese/EN/Y2022/V16/I9/117

Fig.1 Evaluation framework for energy neutrality potential based on element flows inside a model wastewater treatment plant.

Tab.1 Initial variables of the framework to evaluate the energy neutrality potential of a wastewater treatment plant

Tab.2 Classification of the energy neutrality potential of wastewater treatment plants

Fig.2 Frequency of WWTP distribution in intervals of energy self-sufficiency and comprehensive water–energy efficiency.

Fig.3 Comparative analysis of variables for fully/non-self-sufficient and benchmark/normal wastewater treatment plants.

Fig.4 Classification of the energy neutrality potential of 970 wastewater treatment plants.

Cluster of energy neutrality potential	Sample number (Proportion rate)			Chi² test
Cluster of energy neutrality potential	Upstream	Midstream	Downstream	$χ 2$	p-value
High	78 (33.1%)	87 (31.8%)	111 (24.1%)	101.601	<0.001
Medium I	36 (15.3%)	105 (38.3%)	68 (14.8%)
Medium II	67 (28.4%)	22 (8.0%)	121 (26.3%)
Low	55 (23.3%)	60 (21.9%)	160 (34.8%)

Tab.3 Number and proportion of wastewater treatment plants with different energy neutrality potential in the subregions

Fig.5 Characteristics of energy neutrality potential: (a) net energy recovery and (b) discharge condition.

Explanatory factor	Mean rank in each cluster			Kruskal–Wallis H test
Explanatory factor	Low	Medium	High	$χ 2$	p-value
Treatment capacity (10⁴ m³/d)	351.01	510.76	581.15	98.956	<0.001
Sludge production (kg/a)	393.53	516.31	530.37	41.780	<0.001
Influent COD concentration (mg/L)	420.12	491.18	542.01	26.382	<0.001
Influent BOD₅/COD	430.65	491.69	530.75	17.949	<0.001
Influent COD/TN	486.05	504.51	456.09	4.973	0.083
Influent BOD₅/TP	488.36	479.35	491.98	0.378	0.828

Tab.4 Analysis of explanatory factors with different types of energy neutrality potential

Fig.6 Sensitivity analysis on variables of energy consumed and recovered.

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