The comprehensive analysis and research on the selection and evaluation of technology for urban black and odorous water remediation have not yet formed a complete system, and the technical analysis and comparison of the remediation technology are not combined with the characteristics of the river and the pollution status, which often could not achieve the expected effect. Combining the multi-level index division and fuzzy weight matrix calculation method, this paper establishes a comprehensive evaluation method for urban black–odorous water treatment technology based on multi-level fuzzy analysis. The proposed method was applied to assess four kinds of in situ purification-aquatic plant remediation technologies. The results showed that the pollutants removal efficiency of a submerged plant was much higher than that of an emergent aquatic plant, floating-leaved water plant and floating plant. Meanwhile, according to the evaluation model, the comprehensive grading order of in situ purification-aquatic plants was as follows: emergent aquatic plant (84.2044) > submerged plant (78.838) > floating-leaved water plant (72.7596) > floating plant (66.4312). The calculations indicated that the ecological restoration project of black and odorous water should build an ecological restoration technology system based on in situ purification-submerged plant remediation technology, supplemented by other three types of aquatic phytoremediation technologies.

  • This study establishes a comprehensive evaluation method for urban black–odorous water treatment technology based on multi-level index division and fuzzy weight matrix calculation.

  • The black–odorous water treatment technology was divided into six categories.

  • The ecological restoration project of black and odorous water should be constructed mainly by in situ purification-submerged plant remediation technology.

Graphical Abstract

Graphical Abstract
Graphical Abstract

The phenomenon of black–odorous water arises as one of the most significant water environment problems, which adversely damages eco-environmental quality, urban landscape and citizen health (Yekta et al. 2015; Zhou et al. 2016; Zhang et al. 2018). Therefore, the urban black–odorous water treatment is a systematic work, and the treatment scheme should be formulated scientifically according to the actual situation. Numerous studies have put forward and classified a series of alternative remediation technology including pollution interception and source control, sediment dredging, active water circulation and ecological remediation (Xu et al. 2018; Yao et al. 2020; Wang et al. 2021; Xia et al. 2022). However, there is a lack of selection methods for various treatment technologies (Shan et al. 2009; Sinha & Lobiyal 2013; Wang et al. 2020). At present, in the process of black–odorous water treatment, technical analysis and comparison are not carried out in combination with factors such as river characteristics and the current situation of river pollution, which often cannot reach the anticipated result (Schlötelburg et al. 2019; Sarigai et al. 2021). Accordingly, in order to select suitable, efficient and economical treatment measures among numerous technologies, the first thing to be done is to select an appropriate method to evaluate the existing technologies. Technology assessment is an essential step for technology application and the determination of the best feasible technical route (Liu et al. 2017; Li et al. 2020; Lin et al. 2021).

In the process of black–odorous water treatment, there is increasing concern about the formation mechanism of black and odorous, the applied ways of water treatment technology, the construction of water ecological environment and the evaluation effect of water environment treatment (Li et al. 2019; Cai & Larese-Casanova 2020; Li et al. 2021). However, the comprehensive analysis for the selection and evaluation of technologies before urban black–odorous water remediation has not yet formed a complete index system (Li et al. 2016; Cao et al. 2020). Therefore, special attention should be paid to the research on the evaluation system of water treatment technology. Considering that there are many influencing factors in the application of urban black–odorous water remediation technology, and the focus is on eliminating foul water, improving water quality, restoring river ecosystem and improving the living environment, therefore, the evaluation of treatment technology should mainly focus on technical applicability, economic rationality, efficient treating effect and environmental improvement (Jin et al. 2006; Kong et al. 2017; Chen et al. 2020). A multi-level fuzzy analysis method can be used for the technical evaluation of black–odorous water, which not only solves the complex operation of the fuzzy comprehensive evaluation method, but also solves the influence of subjective fuzziness on decision-making in the analytic hierarchy process (Feng et al. 2010; Fan et al. 2019; Chen et al. 2021).

Combining multi-level index division and the fuzzy weight matrix calculation method, the aim of this paper was to establish a comprehensive evaluation method for urban black–odorous water treatment technology based on multi-level fuzzy analysis. The process of the evaluation method is as follows. Firstly, combined with the classification of black and odorous water remediation technology, a multi-dimensional evaluation index system including economic indicators, technical indicators, environmental indicators is constructed. Secondly, the index weights and grading assignment standards are determined. Finally, a fuzzy relation matrix is used to calculate the score of black–odorous water treatment technology. The established comprehensive evaluation method was used to evaluate the in situ aquatic plant remediation technology, which proved the evaluation method was effective and reliable. The technical evaluation index system considered the diversity and applicability of treatment technology for urban black–odorous water, aiming to provide a reference for the selection and comprehensive evaluation of black–odorous water treatment technologies.

Construction of a comprehensive evaluation system

A practical and comprehensive evaluation system of urban black–odorous water treatment technology should have the following characteristics. The applicability of the same type of technology can be evaluated by design or technical parameters. The evaluation method can evaluate the technology both qualitatively and quantitatively. The evaluation method is simple and practical, and easy to be popularized in the evaluation of urban black–odorous water treatment technology in China. The evaluation results are dependable and intuitive, which can reflect water quality succinctly and clearly.

When evaluating urban black–odorous water treatment technology, the technology is classified firstly and the index systems suitable for different types of treatment technology is established. Secondly, the evaluation steps and key points of different treatment technology are determined. Finally, the in situ aquatic plant remediation technology is verified by the evaluation system to prove the applicability of the comprehensive evaluation system. Combined with a fuzzy comprehensive evaluation and analytic hierarchy process, a simple and comprehensive evaluation system of urban black–odorous water treatment technology is established. The technical route of the evaluation method for urban black–odorous water treatment technology is shown in Figure 1.
Figure 1

The technical route of the evaluation method for urban black–odorous water treatment technology.

Figure 1

The technical route of the evaluation method for urban black–odorous water treatment technology.

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Classification of urban black–odorous water treatment technology

Before the evaluation of water treatment technology, it is necessary to classify various technology. According to different treatment purposes and directions, black–odorous water treatment technology can be divided into the following categories: sewage interception, rainfall–runoff pollution control, sediment pollution control, ecological restoration, water purification and living water circulation. Different classes of treatment techniques are applicable to different scopes of governance. The summary of remediation technology for urban black–odorous water is shown in Table 1.

Table 1

Summary of remediation technology for urban black–odorous water

Remediation TechnologyApplication RangeTechnical Approach
Sewage interception Direct discharge of sewage in fair weather Sewage interception-sewage treatment plant, Sewage interception-sewage treatment plant-in situ wastewater treatment 
Rainfall–runoff pollution control Pollution control of combined sewerage overflow, Pollution control of separate sewer discharge Low impact development measures, Rainwater rapid purification technologies (cyclone sand settling technique, rotary centrifugal technique, magnetic separation technique, rapid filtration technique), Rainwater storage tanks, Constructed wetland 
Sediment pollution control Sediment dredging Drainage and dredging technique, Underwater dredging technique, In situ remediation 
Sediment disposal Vacuum dewatering technique, Centrifugal dehydration technique, Plate and frame filter pressure filtration dehydration technique, Belt pressure filtration dehydration technique 
Ecological restoration Revetment ecologic restoration Flinty riparian-ecotype channel bottom, Ecological revetment-ecotype channel bottom, Semi-ecological revetment – ecotype channel bottom, All flinty riparian 
Water purification Bypass purification Coagulation filtration technique, Magnetic coagulation technique, Stabilization pond system, Surface flow wetland, Subsurface flow wetland, Biological contact oxidation process 
In-situ purification Aeration and oxygenation technique, Biological carrier filler (carrier filler-aeration, carrier filler-micro aeration, aquatic plant root purification), Aquatic plants in-situ remediation (emergent aquatic plant, submerged plant, floating-leaved plant, floating plant) 
Living water circulation Drawing water to river Reused water, Surface water, Rainwater 
Remediation TechnologyApplication RangeTechnical Approach
Sewage interception Direct discharge of sewage in fair weather Sewage interception-sewage treatment plant, Sewage interception-sewage treatment plant-in situ wastewater treatment 
Rainfall–runoff pollution control Pollution control of combined sewerage overflow, Pollution control of separate sewer discharge Low impact development measures, Rainwater rapid purification technologies (cyclone sand settling technique, rotary centrifugal technique, magnetic separation technique, rapid filtration technique), Rainwater storage tanks, Constructed wetland 
Sediment pollution control Sediment dredging Drainage and dredging technique, Underwater dredging technique, In situ remediation 
Sediment disposal Vacuum dewatering technique, Centrifugal dehydration technique, Plate and frame filter pressure filtration dehydration technique, Belt pressure filtration dehydration technique 
Ecological restoration Revetment ecologic restoration Flinty riparian-ecotype channel bottom, Ecological revetment-ecotype channel bottom, Semi-ecological revetment – ecotype channel bottom, All flinty riparian 
Water purification Bypass purification Coagulation filtration technique, Magnetic coagulation technique, Stabilization pond system, Surface flow wetland, Subsurface flow wetland, Biological contact oxidation process 
In-situ purification Aeration and oxygenation technique, Biological carrier filler (carrier filler-aeration, carrier filler-micro aeration, aquatic plant root purification), Aquatic plants in-situ remediation (emergent aquatic plant, submerged plant, floating-leaved plant, floating plant) 
Living water circulation Drawing water to river Reused water, Surface water, Rainwater 

Evaluation index system of urban black–odorous water treatment technology

According to the high standard of systematization and scientization for urban black–odorous water remediation projects, the evaluation index system of urban black–odorous water treatment technology is divided into the following four levels: destination layer, criterion layer, subject layer and evaluation layer. The hierarchical relationship of the evaluation index system is shown in Figure 2.
Figure 2

The hierarchical relationship of the evaluation index system for urban black–odorous water treatment technology.

Figure 2

The hierarchical relationship of the evaluation index system for urban black–odorous water treatment technology.

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Multilevel fuzzy comprehensive evaluation model

The multi-level fuzzy comprehensive evaluation model consists of evaluated object, index set, weight set, judgment matrix and fuzzy comprehensive judgment set. Firstly, the index and weight set are established through the index and weight of the evaluated object. Secondly, the single-factor membership degree function of each level is determined to get the membership degree of the evaluation index for each level. Finally, the final evaluation result is obtained through the matrix multiplication calculation which is calculated by the fuzzy comprehensive evaluation set.

The evaluation steps of the multi-level fuzzy comprehensive evaluation model are shown in Figure 3.
Figure 3

The evaluation steps of the multi-level fuzzy comprehensive evaluation model.

Figure 3

The evaluation steps of the multi-level fuzzy comprehensive evaluation model.

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Step 1: Determine the factor set of the evaluation object

Let U = {u1, u2, ···, um} be the evaluated factor set (rating indicator). Where m is the number of evaluation factors, which is determined by the specific evaluation system. For the convenience of weight distribution and evaluation, each category is regarded as a single evaluation factor, and is called the first-level evaluation factor. The first-level evaluation factor can set the subordinate's second level evaluation factor, and so on.
where Ui = {ui1, ui2, … , uim}, UiUj = ф, any ij. {Ui} is a partition of U, and Ui is called a class (or block).

Step 2: Determine the set of comments for evaluation object

Let V = {v1, v2, ···, vn} be the set of evaluation grades composed of various general evaluation results that the evaluator may make for the evaluated object. Here, vj represents the evaluation result, j = 1, 2, 3, ···, n. n is the total number of evaluation results which are generally divided into 3–5 grades.

Step 3: Determine the weight vector of evaluation factors

Let A = {a1, a2, ···, an} be the weight allocation fuzzy vector, where ai represents the factor weight requiring ai > 0 and ∑ai = 1. A reflects the importance of each factor. The weight determination methods mainly include the analytic hierarchy process, weighted average method, expert evaluation method, and Eigenvalue method.

Step 4: Establish the fuzzy relation matrix R through the single factor fuzzy evaluation

Evaluate from a single factor to determine the subjection degree of evaluation object to evaluation set V. After constructing the hierarchical fuzzy subsets, it is necessary to quantify the evaluated objects from each factor one by one, and then determine the membership degree of evaluated objects to each hierarchical fuzzy subset, and finally obtain the fuzzy relation matrix:
where rij represents the membership degree of an evaluated object to the fuzzy subset vj of grade from the perspective of factor ui. The performance of an evaluated object in terms of a factor ui is characterized by the fuzzy vector ri. The ri is called evaluation matrix, which can be regarded as a fuzzy relationship between factor set U and evaluation set V. The ‘reasonable relationship’ between the influencing factors and the evaluation objects.

Step 5: Multi-index comprehensive evaluation (synthetic fuzzy comprehensive evaluation result vector)

The fuzzy comprehensive evaluation result of vector B for each evaluated object is obtained by combining fuzzy vector A and fuzzy relation matrix R through an appropriate fuzzy synthesis operator. The fuzzy comprehensive evaluation model is:
where bj represents the membership degree of fuzzy subset element vj for evaluation grade corresponding to the evaluated object. The ‘ο’ is a fuzzy operator.

Step 6: Analyze the results of fuzzy comprehensive evaluation

The result of fuzzy comprehensive evaluation is the membership degree of fuzzy subset for each grade, which is generally a fuzzy vector rather than a point value, so it can provide more information than other methods. To compare and sort multiple evaluation objects, further processing is required. First, calculate the comprehensive score of each evaluation object, then sort by size, and finally choose the best in order. The comprehensive evaluation result B is converted to the comprehensive score value, so that it can be sorted by size to select the best one.

In order to understand and compare the aquatic phytoremediation technologies better, and verify the science and applicability of the comprehensive evaluation method for urban black-odor water treatment technology, this paper selected the in situ purification-aquatic plant remediation technology for evaluation. In situ purification technology mainly includes in situ purification-emergent aquatic plant remediation technology, in situ purification-submerged plant remediation technology, in situ purification-floating-leaved water plant remediation technology, in situ purification-floating plant remediation technology. Therefore, four types of in-situ purification technology were evaluated in this paper to understand the aquatic plant remediation technology comprehensively, and then select different types of in situ purification-aquatic plant remediation technology according to different objectives.

The classification of an evaluation factor set

According to the evaluation steps of the comprehensive evaluation method for urban black-odor water treatment technology, the evaluation index system of in situ purification-aquatic plant remediation technology was firstly determined, and then the evaluation factor set was determined. The factor set was divided into three levels. The evaluation index system is shown in Figure 4.
Figure 4

The evaluation index system of in situ purification-aquatic plant remediation technology.

Figure 4

The evaluation index system of in situ purification-aquatic plant remediation technology.

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The comments of an evaluation factor set

According to the evaluation steps of the evaluation model for urban black and odorous water remediation technology, the comment set described in this part corresponds to the comments set V in step 2 of chapter 2.4. The comments of evaluation factor set for in situ purification-aquatic plant remediation technology need to be determined according to the actual situation. The comments set V = {perfectly reasonable, fairly reasonable, reasonable, unreasonable} is adopted, and the total score of the four comments is 1.

The determination of each level weight

According to the evaluation steps of the evaluation model of urban black and odorous water remediation technology, the weight vector described in this part corresponds to the weight vector V in step 3 of chapter 2.4. The weight vector value represents the importance degree of each factor in the factor set, and the sum of the weights is 1. According to the application of in situ purification-aquatic plant remediation technology in practical engineering, each level weight of factors was determined respectively, and then the fuzzy weight distribution vector A was established, which reflected the importance of each factor. Each level weight of evaluation index system for in situ purification-aquatic plant remediation technology is shown in Table 2.

Table 2

Each level weight of evaluation index system for in situ purification-aquatic plant remediation technology

First levelWeightSecond levelWeightThird levelWeight
Economic indicator 0.4 Investment cost 0.2 Infrastructural project cost 
Operational cost 0.8 Manpower cost 0.4 
Depreciation cost 0.6 
Technical indicator 0.6 Treatment effect 0.6 Pollutant removal efficiency 0.2 
Odor control level 0.1 
Transparency improvement 0.2 
Dissolved oxygen enhancement 0.2 
Ammonia nitrogen removal 0.2 
ORP promotion 0.1 
Technical suitability 0.2 Occupied area 0.2 
Construction cycle 0.2 
Operational cycle 0.3 
Security risk 0.3 
Environmental benefit 0.2 Landscape effect 
First levelWeightSecond levelWeightThird levelWeight
Economic indicator 0.4 Investment cost 0.2 Infrastructural project cost 
Operational cost 0.8 Manpower cost 0.4 
Depreciation cost 0.6 
Technical indicator 0.6 Treatment effect 0.6 Pollutant removal efficiency 0.2 
Odor control level 0.1 
Transparency improvement 0.2 
Dissolved oxygen enhancement 0.2 
Ammonia nitrogen removal 0.2 
ORP promotion 0.1 
Technical suitability 0.2 Occupied area 0.2 
Construction cycle 0.2 
Operational cycle 0.3 
Security risk 0.3 
Environmental benefit 0.2 Landscape effect 

The scores of comments set

According to the practical application of the four in situ purification-aquatic plant remediation technologies, the evaluation criteria and scoring values of the third-level evaluation factors were first determined. Secondly, the evaluation basis of the third-level evaluation factors for different types of aquatic plants was determined. Then, according to the scoring standard and basis, the evaluation set of in situ purification-aquatic plant remediation technologies was assigned numerically to determine the scoring situation. Finally, the fuzzy relation matrix R was established, that is, the evaluation step 4 of the evaluation model for urban black–odorous water treatment technology. The scoring criteria, scoring basis and scoring for the four technical comment sets are shown in Tables 3 and 4, respectively.

Table 3

The scoring criteria and scoring basis for the four technical comment sets

Third levelScoring criteriaScores
Practical application
[0–0.2)0.2–0.40.4–0.60.6–0.80.8–1Emergent aquatic plantSubmerged plantFloating-leaved water plantFloating plant
Infrastructural project cost Cost of purchasing plants and supporting materials (CNY/m250–350 50–250 50–200 50–150 10–100 0–200 0–120 0–300 0–250 
Manpower cost Salvage maintenance cost (CNY/m2·y) >10 7.5–10 5–7.5 2.5–5 0–2.5 0–4 0–2 0–5 0–6 
Depreciation cost Replant plant (CNY/m2100 40–100 20–80 20–60 0–20 0–30 0–10 0–60 0–80 
Pollutant removal efficiency CODcr removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–5 10–25 5–15 0–10 
TN removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–10 15–35 10–20 0–12 
TP removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–10 20–35 10–25 0–15 
Odor control level Deodorization capacity (0–10) 0–2 0–4 0–6 0–8 0–10 0–6 0–8 0–2 0–3 
Transparency improvement Improve transparency (cm) 0–20 0–40 0–60 0–80 >100 0–20 30–150 0–20 20–100 
Dissolved oxygen enhancement Unit oxygenation effect (mg/L) 0–2 0–4 0–6 0–8 >10 0–5 5–10 2–6 4–8 
Ammonia nitrogen removal Ammonia removal rate (%) 0–10 0–30- 0–50 0–70 0–100 0–10 10–25 5–15 0–13 
ORP promotion ORP enhancement effect (mV) 0–20 0–40 0–60 0–80 >100 0–25 30–100 10–40 20–40 
Occupied area Influence water space range Water surface Water top Water top and middle Water top, middle and bottom Total position of water River shore Water bottom Water surface and bottom Water surface 
Construction cycle Plant area per unit time (d/100 m2>6 0–6 0–4 0–2 0–1 0–1.5 0–0.8 0–1.2 0–1 
Operational cycle Maintenance intervals (times/y) 0–2.5 0–2 0–1.5 0–1 0–0.5 0.3–0.5 1–2 0.5–0.6 1–3 
Security risk Pollution load of plant residues entering water (mg/kg) >200 0–200 0–150 0–100 0–50 0–250 0–100 0–150 0–350 
Landscape effect Landscape index (0–10) 0–2 0–4 0–6 0–8 0–10 0–5 0–4 0–8 0–5 
Third levelScoring criteriaScores
Practical application
[0–0.2)0.2–0.40.4–0.60.6–0.80.8–1Emergent aquatic plantSubmerged plantFloating-leaved water plantFloating plant
Infrastructural project cost Cost of purchasing plants and supporting materials (CNY/m250–350 50–250 50–200 50–150 10–100 0–200 0–120 0–300 0–250 
Manpower cost Salvage maintenance cost (CNY/m2·y) >10 7.5–10 5–7.5 2.5–5 0–2.5 0–4 0–2 0–5 0–6 
Depreciation cost Replant plant (CNY/m2100 40–100 20–80 20–60 0–20 0–30 0–10 0–60 0–80 
Pollutant removal efficiency CODcr removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–5 10–25 5–15 0–10 
TN removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–10 15–35 10–20 0–12 
TP removal rate (%) 0–10 0–30 0–50 0–70 0–100 0–10 20–35 10–25 0–15 
Odor control level Deodorization capacity (0–10) 0–2 0–4 0–6 0–8 0–10 0–6 0–8 0–2 0–3 
Transparency improvement Improve transparency (cm) 0–20 0–40 0–60 0–80 >100 0–20 30–150 0–20 20–100 
Dissolved oxygen enhancement Unit oxygenation effect (mg/L) 0–2 0–4 0–6 0–8 >10 0–5 5–10 2–6 4–8 
Ammonia nitrogen removal Ammonia removal rate (%) 0–10 0–30- 0–50 0–70 0–100 0–10 10–25 5–15 0–13 
ORP promotion ORP enhancement effect (mV) 0–20 0–40 0–60 0–80 >100 0–25 30–100 10–40 20–40 
Occupied area Influence water space range Water surface Water top Water top and middle Water top, middle and bottom Total position of water River shore Water bottom Water surface and bottom Water surface 
Construction cycle Plant area per unit time (d/100 m2>6 0–6 0–4 0–2 0–1 0–1.5 0–0.8 0–1.2 0–1 
Operational cycle Maintenance intervals (times/y) 0–2.5 0–2 0–1.5 0–1 0–0.5 0.3–0.5 1–2 0.5–0.6 1–3 
Security risk Pollution load of plant residues entering water (mg/kg) >200 0–200 0–150 0–100 0–50 0–250 0–100 0–150 0–350 
Landscape effect Landscape index (0–10) 0–2 0–4 0–6 0–8 0–10 0–5 0–4 0–8 0–5 
Table 4

The scoring for the four technical comment sets

Third levelScoring criteriaTechnologiesPerfectly reasonableFairly reasonableReasonableUnreasonable
Infrastructural project cost Cost of purchasing plants and supporting materials (CNY/m2T1 0.6 0.2 0.2 
T2 0.6 0.2 0.1 0.1 
T3 0.1 0.2 0.3 0.4 
T4 0.2 0.3 0.3 0.2 
Manpower cost Salvage maintenance cost (CNY/m2·y) T1 0.3 0.3 0.2 0.2 
T2 0.5 0.3 0.1 0.1 
T3 0.2 0.4 0.3 0.1 
T4 0.1 0.2 0.4 0.3 
Depreciation cost Replant plant (CNY/m2T1 0.6 0.2 0.2 
T2 0.8 0.1 0.1 
T3 0.4 0.2 0.2 0.2 
T4 0.4 0.1 0.3 0.2 
Pollutant removal efficiency CODcr removal rate (%) T1 0.1 0.3 0.4 0.2 
T2 0.4 0.3 0.2 0.1 
T3 0.3 0.3 0.2 0.2 
T4 0.2 0.3 0.4 0.1 
TN removal rate (%) T1 0.2 0.2 0.4 0.2 
T2 0.4 0.4 0.1 0.1 
T3 0.2 0.4 0.2 0.2 
T4 0.2 0.4 0.1 0.3 
TP removal rate (%) T1 0.2 0.2 0.3 0.3 
T2 0.5 0.3 0.1 0.1 
T3 0.4 0.2 0.3 0.1 
T4 0.2 0.2 0.4 0.2 
Odor control level Deodorization capacity (0–10) T1 0.5 0.2 0.2 0.1 
T2 0.6 0.1 0.2 0.1 
T3 0.3 0.3 0.2 0.2 
T4 0.2 0.3 0.4 0.1 
Transparency improvement Improve transparency (cm) T1 0.2 0.3 0.3 0.2 
T2 0.5 0.3 0.2 
T3 0.2 0.3 0.3 0.2 
T4 0.3 0.3 0.2 0.2 
Dissolved oxygen enhancement Unit oxygenation effect (mg/L) T1 0.2 0.3 0.3 0.2 
T2 0.5 0.2 0.2 0.1 
T3 0.1 0.2 0.4 0.3 
T4 0.3 0.2 0.3 0.2 
Ammonia nitrogen removal Ammonia removal rate (%) T1 0.1 0.2 0.3 0.4 
T2 0.2 0.3 0.4 0.1 
T3 0.2 0.4 0.2 0.2 
T4 0.2 0.3 0.3 0.2 
ORP promotion ORP enhancement effect (mV) T1 0.3 0.2 0.2 0.3 
T2 0.6 0.2 0.1 0.1 
T3 0.4 0.3 0.2 0.1 
T4 0.5 0.2 0.2 0.1 
Occupied area Influence water space range T1 0.1 0.3 0.3 0.3 
T2 0.3 0.3 0.2 0.2 
T3 0.4 0.3 0.2 0.1 
T4 0.2 0.3 0.2 0.3 
Construction cycle Plant area per unit time (d/100 m2T1 0.2 0.3 0.3 0.2 
T2 0.5 0.3 0.1 0.1 
T3 0.3 0.3 0.3 0.1 
T4 0.4 0.3 0.2 0.1 
Operational cycle Maintenance intervals (times/y) T1 0.8 0.1 0.1 
T2 0.6 0.2 0.1 0.1 
T3 0.4 0.3 0.1 0.2 
T4 0.3 0.2 0.3 0.2 
Security risk Pollution load of plant residues entering water (mg/kg) T1 0.2 0.2 0.3 0.3 
T2 0.6 0.2 0.2 
T3 0.5 0.3 0.1 0.1 
T4 0.3 0.2 0.2 0.3 
Landscape effect Landscape index (0–10) T1 0.5 0.3 0.1 0.1 
T2 0.3 0.3 0.3 0.1 
T3 0.8 0.1 0.1 
T4 0.5 0.3 0.1 0.1 
Third levelScoring criteriaTechnologiesPerfectly reasonableFairly reasonableReasonableUnreasonable
Infrastructural project cost Cost of purchasing plants and supporting materials (CNY/m2T1 0.6 0.2 0.2 
T2 0.6 0.2 0.1 0.1 
T3 0.1 0.2 0.3 0.4 
T4 0.2 0.3 0.3 0.2 
Manpower cost Salvage maintenance cost (CNY/m2·y) T1 0.3 0.3 0.2 0.2 
T2 0.5 0.3 0.1 0.1 
T3 0.2 0.4 0.3 0.1 
T4 0.1 0.2 0.4 0.3 
Depreciation cost Replant plant (CNY/m2T1 0.6 0.2 0.2 
T2 0.8 0.1 0.1 
T3 0.4 0.2 0.2 0.2 
T4 0.4 0.1 0.3 0.2 
Pollutant removal efficiency CODcr removal rate (%) T1 0.1 0.3 0.4 0.2 
T2 0.4 0.3 0.2 0.1 
T3 0.3 0.3 0.2 0.2 
T4 0.2 0.3 0.4 0.1 
TN removal rate (%) T1 0.2 0.2 0.4 0.2 
T2 0.4 0.4 0.1 0.1 
T3 0.2 0.4 0.2 0.2 
T4 0.2 0.4 0.1 0.3 
TP removal rate (%) T1 0.2 0.2 0.3 0.3 
T2 0.5 0.3 0.1 0.1 
T3 0.4 0.2 0.3 0.1 
T4 0.2 0.2 0.4 0.2 
Odor control level Deodorization capacity (0–10) T1 0.5 0.2 0.2 0.1 
T2 0.6 0.1 0.2 0.1 
T3 0.3 0.3 0.2 0.2 
T4 0.2 0.3 0.4 0.1 
Transparency improvement Improve transparency (cm) T1 0.2 0.3 0.3 0.2 
T2 0.5 0.3 0.2 
T3 0.2 0.3 0.3 0.2 
T4 0.3 0.3 0.2 0.2 
Dissolved oxygen enhancement Unit oxygenation effect (mg/L) T1 0.2 0.3 0.3 0.2 
T2 0.5 0.2 0.2 0.1 
T3 0.1 0.2 0.4 0.3 
T4 0.3 0.2 0.3 0.2 
Ammonia nitrogen removal Ammonia removal rate (%) T1 0.1 0.2 0.3 0.4 
T2 0.2 0.3 0.4 0.1 
T3 0.2 0.4 0.2 0.2 
T4 0.2 0.3 0.3 0.2 
ORP promotion ORP enhancement effect (mV) T1 0.3 0.2 0.2 0.3 
T2 0.6 0.2 0.1 0.1 
T3 0.4 0.3 0.2 0.1 
T4 0.5 0.2 0.2 0.1 
Occupied area Influence water space range T1 0.1 0.3 0.3 0.3 
T2 0.3 0.3 0.2 0.2 
T3 0.4 0.3 0.2 0.1 
T4 0.2 0.3 0.2 0.3 
Construction cycle Plant area per unit time (d/100 m2T1 0.2 0.3 0.3 0.2 
T2 0.5 0.3 0.1 0.1 
T3 0.3 0.3 0.3 0.1 
T4 0.4 0.3 0.2 0.1 
Operational cycle Maintenance intervals (times/y) T1 0.8 0.1 0.1 
T2 0.6 0.2 0.1 0.1 
T3 0.4 0.3 0.1 0.2 
T4 0.3 0.2 0.3 0.2 
Security risk Pollution load of plant residues entering water (mg/kg) T1 0.2 0.2 0.3 0.3 
T2 0.6 0.2 0.2 
T3 0.5 0.3 0.1 0.1 
T4 0.3 0.2 0.2 0.3 
Landscape effect Landscape index (0–10) T1 0.5 0.3 0.1 0.1 
T2 0.3 0.3 0.3 0.1 
T3 0.8 0.1 0.1 
T4 0.5 0.3 0.1 0.1 

T1 represents the in situ purification-emergent aquatic plant. T2 represents the in situ purification-submerged plant. T3 represents the in situ purification-floating-leaved water plant. T4 represents the in situ purification-floating plant.

The scores of the evaluation index

The single-factor fuzzy evaluation was carried out by combining the fuzzy relation matrix R, which was composed of the evaluation set score values for each in situ purification-aquatic plant remediation technology, with the factor weight. The fuzzy relation matrix was established, and the evaluation set vector results of the evaluation set for the subject layer and the criterion layer were obtained. At the same time, the evaluation vector results and evaluation set were weighted to obtain the comprehensive score of each factor in the evaluation model.

The comprehensive evaluation of in situ purification-aquatic plant remediation technology

The comprehensive scoring results of the four technologies are summarized in Table 5. To better compare the emphasis of various technologies on economic factors, technical factors and environmental factors, the scoring of the subject layer (the second layer) is summarized as a radar chart, as shown in Figure 5.
Table 5

The comprehensive scoring results of the four technologies

Destination layerScoresCriterion layer (First level)ScoresSubject layer (Second level)Scores
In situ purification-emergent aquatic plant 78.838 Economic indicator 84.04 Investment cost 89 
Operational cost 82.8 
Technical indicator 75.37 Treatment effect 66.8 
Technical suitability 91.95 
Environmental benefit 84.5 
In situ purification-submerged plant 84.2044 Economic indicator 90.7 Investment cost 91.5 
Operational cost 90.5 
Technical indicator 79.874 Treatment effect 79.59 
Technical suitability 84.10 
Environmental benefit 76.5 
In situ purification-floating-leaved water plant 72.7596 Economic indicator 71.4 Investment cost 57 
Operational cost 75 
Technical indicator 73.666 Treatment effect 64.61 
Technical suitability 80 
Environmental benefit 94.5 
In situ purification-floating plant 66.4312 Economic indicator 67.9 Investment cost 69.5 
Operational cost 67.5 
Technical indicator 65.452 Treatment effect 57.22 
Technical suitability 71.1 
Environmental benefit 84.5 
Destination layerScoresCriterion layer (First level)ScoresSubject layer (Second level)Scores
In situ purification-emergent aquatic plant 78.838 Economic indicator 84.04 Investment cost 89 
Operational cost 82.8 
Technical indicator 75.37 Treatment effect 66.8 
Technical suitability 91.95 
Environmental benefit 84.5 
In situ purification-submerged plant 84.2044 Economic indicator 90.7 Investment cost 91.5 
Operational cost 90.5 
Technical indicator 79.874 Treatment effect 79.59 
Technical suitability 84.10 
Environmental benefit 76.5 
In situ purification-floating-leaved water plant 72.7596 Economic indicator 71.4 Investment cost 57 
Operational cost 75 
Technical indicator 73.666 Treatment effect 64.61 
Technical suitability 80 
Environmental benefit 94.5 
In situ purification-floating plant 66.4312 Economic indicator 67.9 Investment cost 69.5 
Operational cost 67.5 
Technical indicator 65.452 Treatment effect 57.22 
Technical suitability 71.1 
Environmental benefit 84.5 
Figure 5

The scoring of the subject layer (the second level).

Figure 5

The scoring of the subject layer (the second level).

Close modal

In terms of treatment effect, the ranking of the four technologies was as follows: in situ purification-submerged plant (79.59) > in situ purification-emergent aquatic plant (66.8) > in situ purification-floating-leaved water plant (64.61) > in situ purification-floating plant (57.22). The score of the submerged plant was the highest, which was significantly different from the other three types of aquatic plants. The results showed that when different types of aquatic plants were used to remove pollutants from water, the removal efficiency of submerged plants was much higher than that of emergent aquatic plants, floating-leaved water plants and floating plants. In terms of technical applicability, the ranking of the four technologies was as follows: in situ purification-emergent aquatic plant (91.95) > in situ purification-submerged plant (84.1) > in situ purification-floating-leaved water plant (80) > in situ purification-floating plant (71.1). Emergent aquatic plant had the highest score, which was significantly different from the other three types of aquatic plants, indicating that emergent plants could be applied to a wide range of different types of water. In terms of operating costs, the ranking of the four technologies was as follows: in situ purification-submerged plant (90.5) > in situ purification-emergent aquatic plant (82.8) > in situ purification-floating-leaved water plant (75) > in situ purification-floating plant (67.5). According to the scores, there was a large difference between the four types of aquatic plants. The operating cost of submerged plants was the lowest, while that of the floating plant was the highest. In terms of investment cost, the ranking of the four technologies was as follows: in situ purification-submerged plant (91.5) > in situ purification-emergent plant (89) > in situ purification-floating plant (69.5) > in situ purification-floating-leaved plant (57), indicating that the submerged plant had the lowest investment, while floating-leaved plant had the highest investment due to its highest ornamental value. In terms of environmental benefits, the ranking of the four technologies was as follows: in situ purification-floating-leaved water plant (94.5) > in situ purification-floating plant (84.5) > in situ purification-submerged plant (82.5) > in situ purification-emergent aquatic plant (76.5). Compared with the other three types of aquatic plants, emergent aquatic plants had the lowest environmental benefits, which was because the evaluation set of environmental benefits was landscape index. The landscape index represented the landscape effect produced by planting aquatic plants in water.

Figure 6 shows the scoring of the criterion layer (the first level) for the in-situ purification-aquatic plant remediation technology. As can be seen from the figure, the score ranking of the economic indicator for the criterion layer (the first level) was as follows: in situ purification-emergent aquatic plant > in situ purification-submerged plant > in situ purification-floating-leaved water plant > in situ purification-floating plant. The score ranking of the technical indicator for the criterion layer (the first level) was the same as the economic indicator. Meanwhile, according to the evaluation model, the comprehensive grading order of in situ purification-aquatic plants was as follows: in situ purification-emergent aquatic plant > in situ purification-submerged plant > in situ purification-floating-leaved water plant > in situ purification-floating plant. The above results showed that the ecological restoration project of black and odorous water should build an ecological restoration technology system based on in situ purification-submerged plant remediation technology, supplemented by other three types of aquatic phytoremediation technologies.
Figure 6

The scoring of the criterion layer (the first level).

Figure 6

The scoring of the criterion layer (the first level).

Close modal

Starting from a systematic theory, this paper constructed a multi-dimensional evaluation index system including economic indicators, technical indicators and environmental indicators based on the classification of black and odorous water remediation technology. Meanwhile, according to the calculation steps of fuzzy weight matrix, the index weights and grading assignment standards were determined. Finally, comprehensive index calculation procedure of urban black–odorous water remediation technology was determined to calculate the score of technologies. The main conclusions of this study were as follows:

  • Through the analysis of a type of urban black–odorous water remediation technology (in situ purification-aquatic plant), the established comprehensive evaluation steps were used to determine the scores of the evaluation indicators for in situ purification-aquatic plant remediation technology, which proved the evaluation method was effective and reliable. The established comprehensive evaluation method could evaluate the urban black–odorous water remediation technology well, which was of great significance to the technical selection and treatment of urban black–odorous water in China.

  • Taking four kinds of in situ purification-aquatic plant remediation technologies (in situ purification-emergent aquatic plant, in situ purification-submerged plant, in situ purification-floating-leaved water plant, in situ purification-floating plant) as examples, the established evaluation method was applied to evaluate each technique comprehensively. In terms of treatment effect, when different types of aquatic plants were used to remove pollutants from water, the removal efficiency of a submerged plant was much higher than the other three types of aquatic plants. In terms of technical applicability, emergent aquatic plants had the highest score, which was significantly different from the other three types of aquatic plants, indicating that emergent plants could be applied to a wide range of different types of water. In terms of operating costs, there was a large difference between the four types of aquatic plants. The operating cost of submerged plants was the lowest, while that of floating plants was the highest. In terms of investment cost, the submerged plant had the lowest investment, while the floating-leaved plant had the highest investment due to its highest ornamental value. In terms of environmental benefits, compared with the other three types of aquatic plants, the emergent aquatic plant had the lowest environmental benefits, which was because the evaluation set of environmental benefits was landscape index, that was, the landscape effect produced by planting aquatic plants in water.

  • According to the evaluation model, the comprehensive grading order of in situ purification-aquatic plants was as follows: in situ purification-emergent aquatic plant (84.2044) > in situ purification-submerged plant (78.838) > in situ purification-floating-leaved water plant (72.7596) > in situ purification-floating plant (66.4312). The results showed that the ecological restoration project of black and odorous water should build an ecological restoration technology system based on in situ purification-submerged plant remediation technology, supplemented by other three types of aquatic phytoremediation technologies.

We are very grateful to the financial support of the China National Critical Project for Science and Technology on Water Pollution Prevention and Control (No. 2017ZX07403001).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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