Characteristics and Resource Recovery Strategies of Solid Waste in Sewerage Systems

: Sewerage systems-related solid waste accumulates in considerable quantities in urban water systems, including rainwater drainage pipes, pumping stations, grease traps, grit chambers, and septic tanks. Traditional management methods, such as sanitary landﬁlling, incineration


Introduction
In recent years, a significant amount of solid waste has accumulated in urban water service pipeline networks and facilities every day [1].Examples include solid waste from rainwater drainage pipes, pumping stations, grease traps, grit chambers, and septic tanks.It seriously affects the normal operation of facilities in sewerage systems.Daily emptying operations are necessary, which leads to the eventual formation of a large amount of solid waste [2,3].In developing countries, the solid waste in sewerage systems is basically not used as a resource.The traditional method of disposal of solid waste from facilities in developing countries is to transport it to landfills.Transportation and landfilling of such solid waste may pose an environmental risk due to its complex composition and a certain quantity of pollutants [4,5].Traditional treatment and disposal methods are no longer viable due to the steady increase in the requirements for environmental protection, and recycling methods suitable for solid waste in developing countries need to be studied.
Research on the disposal and resource utilization of similar solid waste has been extensively conducted, mainly focusing on solid waste generated during the construction process.Table 1 summarizes the treatment purposes and methods of similar solid waste.The treatment purpose of solid waste can be basically divided into three categories, including reduction, resource utilization, and harmless treatment.According to the nature of solid waste and engineering requirements, different methods can be adopted for disposal.For example, when the organic matter content of solid waste is high, thermochemical treatment or anaerobic digestion can be considered to convert it into resources such as natural gas and fertilizer [6][7][8].If the solid waste has good initial mechanical properties, it can be modified by adding lime, cement, fly ash, and other materials to be used as road construction materials [9,10].If the solid waste contains certain harmful components, it is necessary to remove or stabilize these substances, usually using methods such as solidification, stabilization, thermal treatment, separation, and extraction [11][12][13].
Since the solid waste generated during the construction process and the solid waste generated from sewerage systems have similar characteristics, these studies and strategies can be used as references.The solid waste from sewerage systems contains a certain amount of organic matter, which has the potential to be converted into useful products such as biogas or other energy-rich compounds [6][7][8].Solid waste also contains some inorganic components, such as clay, gravel, and fine sand, which can be used as building materials after screening and separating [14,15].Solid waste contains significant levels of nutrients necessary for plant growth, such as nitrogen, phosphorous, potassium, and organic matter.Therefore, when properly treated, it can be used as a soil conditioner and medium-grade fertilizer [16].If solid waste from sewerage systems is properly sorted, it can not only solve the problem of its reduction and disposal, but also generate a lot of valuable resources.However, because solid waste lacks systematic management and strict supervision in developing countries, it is difficult to handle properly.The nature of solid waste from different facilities in sewerage systems is complex and variable.This has made the resource utilization of most solid waste in developing countries difficult.To achieve efficient resource utilization, it is critical to investigate the physical and chemical properties of solid waste and to propose potential resource recovery methods for solid waste in developing countries.

Reduction
Reduce the generation of solid waste Using green building materials [17,18] Reduce the volume after solid waste generation Flocculation, sedimentation, and dewatering [19][20][21] Resource utilization

Reuse as road building materials
Crushing, screening, magnetic sorting, and removal of light materials [9,10] Modified by adding lime, cement, fly ash, silica fume, blast furnace slag, steel slag, rice husk ash, etc. [22][23][24][25][26][27] Reuse as concrete, brick, and ceramic Heating and compressing [28][29][30] Converted to materials such as natural gas and fertilizer Thermochemical treatment or anaerobic digestion [6][7][8] Harmless treatment Remove or stabilize harmful substances Solidification or stabilization [11] Thermal treatment [12] Separation or extraction [13] Based on the above issues, this paper investigated the solid waste generated from different sources of sewerage systems in Shenzhen, China, including solid waste from a sewerage system terminal and representative sites of various sewerage system facilities.The physical and chemical properties of solid waste from various sources in sewerage systems were tested.The corresponding treatment measures and strategies for solid waste in sewerage systems in developing countries were proposed.

Sampling Location
Sewerage systems are composed of various sewerage facilities and terminals.Terminals refer to wastewater treatment plants (WWTP), while sewerage facilities include rainwater drainage pipes, pumping stations, grease traps, grit chambers, septic tanks, etc.In this study, a variety of solid waste from various sources was collected, including the solid Sustainability 2023, 15, 1662 3 of 15 waste from a terminal of sewerage systems and six representative types of solid waste from various facilities in sewerage systems.The sampling location of the terminal of sewerage systems is at the Luofang Water Purification Plant, and the sampling locations of the six different facilities in sewerage systems are at the pipeline network close to the construction site and cuisine street next to the bus stop at the Gangxia Metro Station on Fuhua Road, the pumping station at the Xinzhou Pumping Station, the grease trap and grit chamber close to the Bagualing Refuse Transfer Station, and the septic tank close to Yu Nan Road.The sampling locations shown in Figure 1.
Sewerage systems are composed of various sewerage facilities and terminal nals refer to wastewater treatment plants (WWTP), while sewerage facilities inclu water drainage pipes, pumping stations, grease traps, grit chambers, septic tank this study, a variety of solid waste from various sources was collected, including waste from a terminal of sewerage systems and six representative types of sol from various facilities in sewerage systems.The sampling location of the termina erage systems is at the Luofang Water Purification Plant, and the sampling loc the six different facilities in sewerage systems are at the pipeline network close to struction site and cuisine street next to the bus stop at the Gangxia Metro Station o Road, the pumping station at the Xinzhou Pumping Station, the grease trap and gr ber close to the Bagualing Refuse Transfer Station, and the septic tank close to Road.The sampling locations shown in Figure 1.The samples were collected in pre-cleaned plastic drums and transported t boratory at a low temperature.The samples were given names based on the s locations, such as LWPP (the samples from Luofang Water Purification Plant), (the sample from the rainwater drainage pipes near the construction site), RDP sample from the rainwater drainage pipes near the cuisine street), PS (the sam the pumping station), GT (the sample from the grease trap), GC (the sample from chamber), and ST (the sample from the septic tank).The samples named LWPP waste separated at various processes, including coarse aggregates, fine aggregat residue, sewage, and substrate.

Solid Waste Characterization
In order to better propose strategies for recycling solid waste of sewerage sy is necessary to test its physical and chemical properties.As shown in Table 2, methods have been adopted to examine the relevant properties of solid waste.In the grille residue and sewage refer to the samples of LWPP.The samples were collected in pre-cleaned plastic drums and transported to the laboratory at a low temperature.The samples were given names based on the sampling locations, such as LWPP (the samples from Luofang Water Purification Plant), RDP-Co (the sample from the rainwater drainage pipes near the construction site), RDP-Cu (the sample from the rainwater drainage pipes near the cuisine street), PS (the sample from the pumping station), GT (the sample from the grease trap), GC (the sample from the grit chamber), and ST (the sample from the septic tank).The samples named LWPP include waste separated at various processes, including coarse aggregates, fine aggregates, grille residue, sewage, and substrate.

Solid Waste Characterization
In order to better propose strategies for recycling solid waste of sewerage systems, it is necessary to test its physical and chemical properties.As shown in Table 2, different methods have been adopted to examine the relevant properties of solid waste.In Table 2, the grille residue and sewage refer to the samples of LWPP.

Codes and Standards
In order to propose a recovery strategy for the solid waste from sewerage systems, the following codes and standards were used to analyze and evaluate its basic properties, as shown in Table 3.Since the sampling location and potential utilization are all in China, the codes and standards selected in this paper are from China.Table 3. Codes and standards for evaluating the nature of solid waste.

Solid Waste Characterization of the Terminal
In order to improve the resource utilization of the samples from the Luofang Water Purification Plant, the composition and properties of the LWPP were examined.Figure 2 shows the composition of LWPP.The mass content of each substance was quantified as a percentage of the total mass.The main component of the separated waste varied, with the coarse aggregates containing mainly stones (60-73%), and other waste such as construction waste (15-30%), foam (5-8%), and slurry (5.9%).The main component within the fine aggregates is sand (81.6%), with other impurities (5.6%) also interspersed.Within the grille residue, there are dead branches and leaves (20-27%), household waste (8-25%), and other organic impurities (64-75%).There is also sewage and substrate produced during the separation process, which is a mixture of water, slurry, and impurities.
Purification Plant, the composition and properties of the LWPP were examined.shows the composition of LWPP.The mass content of each substance was quant percentage of the total mass.The main component of the separated waste varied, coarse aggregates containing mainly stones (60-73%), and other waste such as c tion waste (15-30%), foam (5-8%), and slurry (5.9%).The main component within aggregates is sand (81.6%), with other impurities (5.6%) also interspersed.W grille residue, there are dead branches and leaves (20-27%), household waste and other organic impurities (64-75%).There is also sewage and substrate produ ing the separation process, which is a mixture of water, slurry, and impurities.In addition, physical and chemical property tests were carried out on each of arated waste to determine the pH, water content, heavy metals, and organic m order to lay the foundation for the subsequent determination of the approach to utilization.The properties of coarse aggregates, fine aggregates, grille residue, and substrate are shown in Tables 4 and 5, and Figure 3.The aggregates, grille and substrate all had neutral pH (7-9), no PAHs were found, and the bacteria con comparable to that of common soil (1 × 10 6 ~1 × 10 7 pcs/ g) [47].The sewage contai level of NH3-N (334 mg/L), which does not meet the minimum requirement (N mg/L) of the standard GB 3838-2002 [41].In addition, physical and chemical property tests were carried out on each of the separated waste to determine the pH, water content, heavy metals, and organic matter in order to lay the foundation for the subsequent determination of the approach to resource utilization.The properties of coarse aggregates, fine aggregates, grille residue, sewage, and substrate are shown in Tables 4 and 5, and Figure 3.The aggregates, grille residue, and substrate all had neutral pH (7-9), no PAHs were found, and the bacteria content was comparable to that of common soil (1 × 10 6 ~1 × 10 7 pcs/ g) [47].The sewage contains a high level of NH 3 -N (334 mg/L), which does not meet the minimum requirement (NH 3 -N ≤ 8 mg/L) of the standard GB 3838-2002 [41].In addition, it can be seen from Figure 3 that all the separated wa quantity of heavy metals, and the prospect of resource utilization coarse aggregates contain a high content of Cd (6.5 mg/kg) and the fin a high level of Hg (5.68 mg/kg) and Cd (9.1 mg/kg), which leads to th ing the requirements of the Standard CJ/T340-2016 (Cd ≤ 1.In addition, it can be seen from Figure 3 that all the separated waste contains a certain quantity of heavy metals, and the prospect of resource utilization may be limited.The coarse aggregates contain a high content of Cd (6.5 mg/kg) and the fine aggregates contain a high level of Hg (5.68 mg/kg) and Cd (9.1 mg/kg), which leads to the content far exceeding the requirements of the Standard CJ/T340-2016 (Cd ≤ 1.5 and Hg ≤ 1.8, unit mg/kg) when considering its direct use as soil for planting fill [43].Sewage contains a certain quantity of heavy metals, which may potentially lead to environmental pollution.Since the organic matter content of sewage is not high (30%), it is difficult to utilize it as a resource.Sewage needs to be dewatered and subsequently incinerated.The heavy metals would be enriched in the fly ash and slag produced by incineration, which need to be treated in accordance with the requirements of hazardous waste [48].
The grille residue has high organic matter content (76%).In order to better analyze the approach to resource utilization of the grille residue, some properties such as the volatile matter and ash content of the grille residue were determined, as shown in Table 6.Table 6 shows that the volatile substances, ash, and solid carbon indicators are high.This means that it can be processed into RDF rods.The particle size distribution of coarse aggregates and fine aggregates in LWPP was determined.A 5 mm sieve was used to separate coarse aggregates and fine aggregates, so the particle size of coarse aggregates was greater than 5 mm.The particle size distribution of fine aggregates is shown in Figure 4.The median particle size of fine aggregates is about 0.61 mm, and the content of particles smaller than 0.1 mm is about 10%.Therefore, these materials could be used as a substitute for primary aggregate materials in low specification applications such as road construction and bulk fill.
Sustainability 2023, 15, x FOR PEER REVIEW materials could be used as a substitute for primary aggregate materials in tion applications such as road construction and bulk fill.In summary, a preliminary analysis of resource utilization can be carr waste.The aggregates contain more stones and sand; they can be sieved recover the aggregates for use as road building materials.Due to the high of the grille residue, it can be made into RDF rods for resource utilization.

Solid Waste Characterization in Different Sewerage Facilities
The composition and chemical properties of the solid waste from the ties in sewerage systems were tested.Figures 5-7 show the composition, and heavy metals in the solid waste of each facility.The solid waste RDP large quantity of aggregates (coarse and fine aggregates together accou mately 85% of the total mass) and low organic matter content and heavy m be attributed to the specificity of the sampling area.The rainwater drainag the construction site, and a large amount of cement, gravel, sand, and other have been dumped into the pipe network.
The nature of the solid waste RDP-Cu also has regional characteristi waste has high organic matter content (83%) and a very low content of ag be speculated that some residues of kitchen waste were discharged into drainage pipes.Due to the high organic matter content, it is better to mix with grille residue to make RDF rods.Solid wastes from RDP-Co and In summary, a preliminary analysis of resource utilization can be carried out for each waste.The aggregates contain more stones and sand; they can be sieved and cleaned to recover the aggregates for use as road building materials.Due to the high organic content of the grille residue, it can be made into RDF rods for resource utilization.

Solid Waste Characterization in Different Sewerage Facilities
The composition and chemical properties of the solid waste from the different facilities in sewerage systems were tested.Figures 5-7 show the composition, organic matter, and heavy metals in the solid waste of each facility.The solid waste RDP-Co contains a large quantity of aggregates (coarse and fine aggregates together account for approximately 85% of the total mass) and low organic matter content and heavy metals.This can be attributed to the specificity of the sampling area.The rainwater drainage pipes are near the construction site, and a large amount of cement, gravel, sand, and other building waste have been dumped into the pipe network.
The nature of the solid waste RDP-Cu also has regional characteristics.This type of waste has high organic matter content (83%) and a very low content of aggregates.It can be speculated that some residues of kitchen waste were discharged into the rainwater drainage pipes.Due to the high organic matter content, it is better to mix this solid waste with grille residue to make RDF rods.Solid wastes from RDP-Co and RDP-Cu show strong regional characteristics, which reveals that the degree of management and supervision was insufficient and some wastes were mixed into rainwater drainage pipes.The waste PS, GT, GC, and ST have a high level of aggregates (coarse and fine aggregates together account for about 35-70% of the total mass).Heavy metals are present in higher concentrations.The complexity of the environment near the sampling area may have contributed to this result.Since organic matter and heavy metals are found in the waste, the aggregates in the waste need to be treated by sand washing before recycling.
In summary, the properties of solid waste from different facilities in sewerage systems are obviously different from those at the terminal, and the properties have regional differences, which can be more convenient for resource treatment according to their characteristics.In summary, the properties of solid waste from different facilities in tems are obviously different from those at the terminal, and the propertie differences, which can be more convenient for resource treatment accordin acteristics.

Discussion
This paper has determined the nature of solid waste from various facilities in sewerage systems and put forward preliminary suggestions for resource utilization.In this section, approaches to resource utilization are further discussed in conjunction with relevant regulations.

Approach of Resource Utilization for Solid Waste in Terminal
The results have shown that the nature of solid waste from the WWTP is quite complex, which is not conducive to direct resource utilization.In fact, landfilling has been the main means of disposal of the solid waste in developing countries.However, due to the limited capacity of landfills and the tightening of national policies, landfilling will not be sustainable.Therefore, new approaches need to be discussed and proposed.
In developed countries, the reuse of solid waste in the WWTP according to its nature is the main method of treatment.This method avoids many of the disadvantages of landfilling and is the future trend in the treatment of solid waste.However, the results in Tables 4-6 and Figure 3 show that the nature of solid waste in the WWTP in developing countries is complex, and all types of solid waste produced after separation contain a certain amount of organic matter and heavy metals.It is necessary to first ensure that the content of organic matter and heavy metals in the waste meets the relevant requirements and adopt corresponding approaches to recycle the waste according to its characteristics.
Through multi-stage separation, the solid waste in the WWTP can be classified into coarse aggregates, fine aggregates, grille residue, sewage, and substrate.The approaches to resource utilization are discussed separately.Despite the presence of some heavy metals in the coarse aggregates, the content of heavy metals met the requirements of the Standard DB4403/T 67-2020 [45] for the first category of construction land soil screening values.Therefore, the hazard of coarse aggregates to human health can be ignored when they are used as building materials.According to the requirements related to fillers and bedding layers in the Code JTG D30-2015 [44], the maximum particle size of fillers should be less than 150 mm.As the coarse aggregates contain large aggregates with particle sizes exceeding 150 mm, they are not suitable for direct use as road base fillers.The coarse aggregates need to be crushed to a particle size below 150 mm and then used as roadbed filler.Table 4 and Figure 3 show that low concentrations of heavy metals, normal levels of total bacteria, and no PAHs were detected in fine aggregates.Therefore, there is no need to consider the problem of environmental pollution in the process of utilizing fine aggregates.According to the requirements of the Standard JGJ52-2006 [46], the mud content of the sand should not exceed 2% (Class I), 3% (Class II), and 5% (Class III), respectively [45].Therefore, the fine aggregates need to be cleaned to meet the corresponding requirements for sand.
The main components of the grille residue are dead branches, leaves, and household waste, which contain a large amount of organic matter and has the potential to be used as RDF rods.The general criteria for making RDF rods are as follows: water (<10%), ash (12-25%), volatile matter (55-75%), and solid carbon (7-13%).As can be seen from Table 6, the properties of the grille residue basically meet the requirements, except for the high water content.Therefore, in the subsequent resource utilization of the grille residue, dewatering, crushing, and rod-making processes should be carried out to form the RDF rods.In addition, because of the high organic matter content in the grille residue, the grille residue can also be considered to produce biochar, biocrude, non-condensable flammable gases, and other substances through thermochemical treatment.Alternatively, the grille residue can be mixed with the substrate and fermented through anaerobic digestion to produce biogas and fertilizer.
Figure 3 and Table 5 show that a certain amount of organic matter and heavy metals were detected in the sewage.The organic matter content in sewage is 30%, which is significantly lower than that in developed countries, which is generally about 75% [49].The particularity of the nature of solid waste in the WWTP in developing countries can be seen.Due to the low content of organic matter in sewage, resource utilization methods used in developed countries are difficult to apply directly.According to Code GB 50335-2002 [42], the sewage from the WWTP cannot be used directly for miscellaneous urban water.Sewage needs to be processed before being used, such as through coagulation, sedimentation, filtration, and disinfection.The treated sewage can also be used in the relevant cleaning process in the WWTP.
In summary, the waste separated at various stages in the WWTP can be used resourcefully after secondary treatment.However, the solid waste in the WWTP contains low organic matter content and a certain quantity of heavy metals.This leads to the need to consider pollutants in the process of recycling, which increases the difficulty and cost of disposal.

Approach of Resource Utilization for Solid Waste in Different Sewerage Facilities
From the discussion in Section 4.1, the solid waste in the WWTP can be converted into materials through some means of recycling; however, due to the complexity of the nature of solid waste, the difficulty and cost of recycling have increased.These lead to the fact that in actual operation in developing countries, the solid waste in the WWTP is basically not utilized.
In developing countries, the discharge of solid waste from sewerage systems lacks systematic management and strict supervision, which leads to the complexity of the nature of solid waste in the WWTP.In this case, it is not appropriate to apply the methods of developed countries to the treatment of solid waste related to sewerage systems.Therefore, it is necessary to explore a set of corresponding strategies suitable for the current situation of developing countries.
As can be seen from Figures 5-7, unlike the solid waste taken at the WWTP, the waste collected at the various facilities in sewerage systems have not been mixed or contaminated with each other; therefore, they have distinct characteristics.Based on their properties, the waste collected from the different facilities in sewerage systems can be divided into three categories, as shown in Figure 8A-C: Category A is characterized by a very high sand content and low organic matter content and heavy metals (a representative example is the waste RDP-Co); Category B is characterized by a high sand content but also contains a large number of pollutants (representative examples are the waste from pumping stations, grease traps, septic tanks, and grit chambers); Category C is characterized by a low sand content but a high amount of organic matter and pollutants (a representative example is the waste RDP-Cu).nated with each other; therefore, they have distinct characteristics.Based on their pr ties, the waste collected from the different facilities in sewerage systems can be div into three categories, as shown in Figure 8A-C: Category A is characterized by a very sand content and low organic matter content and heavy metals (a representative exa is the waste RDP-Co); Category B is characterized by a high sand content but also con a large number of pollutants (representative examples are the waste from pumping tions, grease traps, septic tanks, and grit chambers); Category C is characterized by a sand content but a high amount of organic matter and pollutants (a representative e ple is the waste RDP-Cu).As shown in Figure 8, according to the different nature of various types of waste, different approaches of resource utilization can be designed to improve the efficiency of resource utilization of waste.The waste RDP-Co has low organic matter content and pollution and a high sand content.Therefore, it can be utilized as building materials after being dewatered by pressing and filtering.The waste from the pumping stations, grease traps, septic tanks, and grit chambers has a higher pollution level and sand content but a lower organic content.Therefore, the fine aggregates could be recovered through processes such as de-mixing, screening, and sand washing.The sewage generated during the process can be discharged to the WWTP for treatment.The waste from the RDP-Cu has high organic matter content, a high pollution level, and a low sand content, so it can be mixed with the grille residue and then made into RDF rods through filter press dewatering.In addition, the waste of Category C can be mixed with grille residue and treated thermochemically to produce substances such as biochar, biocrude, and non-condensable flammable gases.Anaerobic digestion can also be considered to produce substances such as natural gas and fertilizer, thereby reusing the resource.In the above process, solid waste that does not have resource potential can be discharged to the WWTP for comprehensive treatment.
In summary, the waste collected from different facilities in sewerage systems has not been mixed and has varied greatly in nature, such as the waste RDP-Co, which only requires simple treatment to achieve building materials.The waste RDP-Cu contains high organic matter content and is more suitable for processing into RDF rods.The solid waste generated by these facilities only needs simple treatment to be recycled.Solid waste that is not suitable for recycling can be discharged normally and enter the WWTP for treatment.Through such a strategy, solid waste is sorted in advance and utilized as a resource, which improves the treatment efficiency of solid waste in the sewerage systems and the efficiency of resource utilization.
Pre-sorting, treatment, and recycling of solid waste from sewerage facilities have achieved sustainable development and reduced the pressure on landfill operations.For developing countries, it is a better strategy before management and supervision can meet the requirements.However, for the early sorting and treatment of solid waste, it is necessary to build corresponding treatment facilities, which increases the cost.In the future, it is necessary to conduct analysis from the life-cycle assessment perspective to explain in which specific situations these strategies should be used.

Conclusions
The degree of resource utilization of solid waste generated by the sewerage systems in developing countries is very limited.Based on the idea of sustainable development, it is necessary to expand the methods of resource recovery.In this paper, a variety of waste was collected from a terminal and different facilities in sewerage systems, and the characteristics of solid waste were tested and analyzed.Based on these results, corresponding resource recovery strategies were proposed.The main conclusions are as follows: (1) The waste separated at various stages in the WWTP can be used resourcefully after secondary treatment.Due to weak management and supervision in developing countries, the solid waste contains low organic matter content and a certain quantity of heavy metals, which increases the difficulty and cost of recycling.Therefore, recycling is not recommended until the management level of sewerage systems has been improved; (2) The waste collected from different facilities in sewerage systems has not been mixed and has varied greatly in nature.Before these solid wastes enter the WWTP, the strategy of pre-sorting, treating, and recycling these solid wastes is worth recommending.A small part of solid waste that is not suitable for recycling can be discharged normally and enter the WWTP for treatment.There are three types of solid waste in different sewerage facilities that can be classified.The first category is characterized by an extremely high sand content and low organic matter and heavy metal content, which can be directly used as building materials after dewatering treatment.The second category is characterized by high sand content but also contains a large number of polluting substances which need to be cleaned before being considered as building materials.The third category is characterized by low sand content but high organic matter content and large quantities of polluting substances, which can be dewatered to make RDF rods or undergo thermochemical treatment or anaerobic digestion to become relevant valuable products.
Sustainable development could be accomplished through the pre-sorting, treatment, and recycling of solid waste from sewerage facilities.However, it is necessary to build corresponding treatment facilities for the early classification and treatment of solid waste, which increases the cost.In the future, it is necessary to investigate this topic from a life-cycle-evaluation perspective to clarify when these strategies should be applied.

Figure 1 .
Figure 1.Sampling location: A: Luofang Water Purification Plant; B: rainwater drainage p the construction site); C: rainwater drainage pipes (near the cuisine street); D: pumping grease trap; F: grit chamber; G: septic tank.

Figure 2 .
Figure 2. Composition of solid waste separated at various stages of the terminal.

Figure 2 .
Figure 2. Composition of solid waste separated at various stages of the terminal.

Figure 3 .
Figure 3. Heavy metal content of solid waste separated at various stages of terminal.

Figure 4 .
Figure 4. Particle size distribution of fine aggregates.

Figure 4 .
Figure 4. Particle size distribution of fine aggregates.

Figure 5 .
Figure 5. Inorganic content in solid waste at each facility.

Figure 6 .Figure 6 .
Figure 6.Organic content in solid waste at each facility.

Figure 6 .
Figure 6.Organic content in solid waste at each facility.

Figure 7 .
Figure 7. Heavy metal content in solid waste at each facility.

Figure 7 .
Figure 7. Heavy metal content in solid waste at each facility.

Figure 8 .
Figure 8. Approaches of resource utilization for solid waste in sewerage systems.(A) Category A. (B) Category B. (C) Category C.

Table 1 .
Overview of the treatment and resource utilization of similar solid waste.

Table 2 .
Testing items and reference standards for the nature of solid waste.

Table 4 .
Basic properties of solid waste separated at various stages of terminal.
* ND means that the corresponding substance was not detected in the sample.

Table 5 .
Properties of the sewage.

Table 4 .
Basic properties of solid waste separated at various stages of termin * ND means that the corresponding substance was not detected in the sampl

Table 5 .
Properties of the sewage.

Table 6 .
Properties of the grille residue from the separation process.

Table 6 .
Properties of the grille residue from the separation process.