Abstract

This study has been carried out to evaluate the applicability of the pilot scale hybrid type of stormwater runoff treatment system for treatment of combined sewer overflow. Also, to determine the optimum operation parameter such as coagulation dosage concentration, effectiveness of coagulant usage, surface loading rate and backwashing conditions. The pilot scale stormwater filtration system (SFS) was installed at the municipal wastewater plant serving the city of Cheongju (CWTP), Korea. CWTP has a capacity of 280,000 m3/day. The SFS consists of a hydrocyclone coagulation/flocculation with polyaluminium chloride silicate (PACS) and an upflow filter to treat combined sewer overflows. There are two modes (without PACS use and with PACS use) of operation for the SFS. In case of no coagulant use, the range of suspended solids (SS) and turbidity removal efficiency were 72.0–86.6% (mean 80.0%) and 30.9–71.1% (mean 49.3%), respectively. And, the recovery rate of filter was 79.2–83.6% (mean 81.2%); the rate of remaining solid loading in filter media was 16.4–20.8% (mean 18.8%) after backwashing. The influent turbidity, SS concentrations were 59.0–90.7 NTU (mean 72.0 NTU), 194.0–320.0mg/L (mean 246.7mg/L), respectively. The range of PACS dosage concentration was 6.0–7.1mg/L (mean 6.7mg/L). The range of SS and turbidity removal efficiency was 84.9–98.2 (mean 91.4%) and 70.7–96.3 (mean 84.0%), respectively. It was found that removal efficiency was enhanced with PACS dosage. The recovery rate of filter was 92.0–92.5% (mean 92.3%) the rate of remaining solid loading in filter media was 6.1–8.2% (mean 7.2%) after backwashing. In the case of coagulant use, the particle size of the effluent is bigger than influent particle size. The results showed that SFS with PACS use more effective than without PACS use in SS and turbidity removal efficiency and recovery rate of filter.

INTRODUCTION

A combined sewer system conveys both urban domestic wastewater and stormwater to an end-of-pipe centralized wastewater treatment plant. Combined sewer overflow (CSO) pollution resulting from stormwater runoff has been identified as one of the leading causes of nonpoint pollution (Balmforth 1990; Lee & Bang 2000). CSO is typically composed of wastewater and surface runoff from urbanized areas. Although newly developed areas have separated sewer systems, many of these systems were improperly connected with combined sewers at downstream watersheds. During CSO events, the discharge of untreated sewage and stormwater into local waterways represents a large input of nutrients, organic matter, contaminants, pathogens, debris, etc. (El Samrani et al. 2008). CSO from a large storm event may shock the receiving water body many times greater than an ordinary effluent load, especially during the first flush that occurs in the initial part of the CSO (Sartor et al. 1974; Bedient et al. 1978; Lee & Bang 2000). During storm events, many wastewater treatment plants may not be able to achieve the requested effluent quality. In the worst case, untreated CSO may bypass the plant. To overcome and mitigate these problems related to CSO and stormwater runoff, engineers and others are constantly seeking best management practices (BMPs): filtration, sedimentation, chemical flocculation, and vortex separators. Among the BMPs, the upflow direct filtration system is quite outstanding for sanitary sewer overflow (SSO) and CSO treatment. Many pollutants in CSO are present in the particulate phase, attached to particles transported in suspension, with diameters ranging from a few μm to 1 mm, and a median diameter d50 = 30–40 μm (Torres & Bertrand-Krajewski 2008). Solid particles smaller than 30 μm in diameter are not easily separated by conventional types of upflow filtration system. To overcome this problem, upflow filter combined with hydrocyclone flocculator has been applied to treatment of the microparticles in urban storm runoff (Veolia 2010). Hydrocyclones are widely used as separators or classifiers in chemical, environmental, and mineral processing industries to separate solid particles from a solid–liquid suspension based on the size of particles (Hwang et al. 2008). We have conducted a pilot scale study on the treatable potential of microparticles using a stormwater filtration system (SFS) which used rectangular shape fibre media made of polypropylene and polyethylene materials. This study has been carried out to evaluate the applicability of the pilot scale SFS and determine the optimum operational parameters such as coagulation dosage concentration, effectiveness of coagulant usage, surface loading rate and backwashing conditions. In order to determine the efficiency for various operation conditions, a series of experiments were performed with different particle materials and solid concentrations.

MATERIAL AND METHODS

Setup of the pilot scale stormwater filtration system

The pilot scale stormwater filtration system (SFS) was installed at the municipal wastewater plant serving the city of Cheongju (CWTP) in Korea. CWTP has capacity of 280,000 m3/day. The SFS influent submersible pump was installed at the existing grit chamber. The pilot scale SFS used for the experiments is shown schematically in Figure 1. During a storm event, the discharge of untreated sewage and stormwater are the inflow of CWTP. SFS consisted of two hydrocyclones for coagulation and flocculation, filter column, backwash blower and pump, air flow meter, pressure gauge, valve fitting, centrifugal pump, submersible pumps, automatic switch controller, chemical flowrate gauge, injection pump, electromagnetic flow meter, effluent and underflow storage tank. The design characteristics of SFS are presented in Table 1. Influent submersible pumped from a grit chamber was transfer to the storm water storage tank. Influent from the storm water storage tank was injected to hydrocyclone with coagulant to hydrocyclone and underflow was returned to the influent pipe to improve flocculation ballasting.

Table 1

The design characteristics of stormwater filtration system (SFS)

Item Dimension and specification Capacity 
Raw water pump KSV-4-110 0.8 m3/min 
Influent storage tank PE D2.4 m × H2.8 m 10.0 m3 
Influent pump HANIL PA-2288SS-T 500 L/min 
Flowmeter EMFM HFD3000 0.1–100.0 m3/hr 
Filtration system STS W1.25 m × L0.80 m × H1.8 m 1.4 m3 
Effluent storage tank PE W1.4 m × L1.5 m × H1.35 m 2.0 m3 
Hydrocyclone (coagulation) STS D110 mm × H440 mm 2.1 L 
Hydrocyclone (flocculation) STS D320 mm × H1,280 mm 51.5 L 
Backwash pump KSV-4-75 0.7 m3/min 
Air blower HRB-101(disc diffuser) 1.5 m3/min 
Item Dimension and specification Capacity 
Raw water pump KSV-4-110 0.8 m3/min 
Influent storage tank PE D2.4 m × H2.8 m 10.0 m3 
Influent pump HANIL PA-2288SS-T 500 L/min 
Flowmeter EMFM HFD3000 0.1–100.0 m3/hr 
Filtration system STS W1.25 m × L0.80 m × H1.8 m 1.4 m3 
Effluent storage tank PE W1.4 m × L1.5 m × H1.35 m 2.0 m3 
Hydrocyclone (coagulation) STS D110 mm × H440 mm 2.1 L 
Hydrocyclone (flocculation) STS D320 mm × H1,280 mm 51.5 L 
Backwash pump KSV-4-75 0.7 m3/min 
Air blower HRB-101(disc diffuser) 1.5 m3/min 
Figure 1

Schematic diagram and installation of the pilot scale stormwater filtration system. (a) Schematic diagram, (b) pilot plant installation, and (c) automation system monitor.

Figure 1

Schematic diagram and installation of the pilot scale stormwater filtration system. (a) Schematic diagram, (b) pilot plant installation, and (c) automation system monitor.

Process operation and measurement method

Simulated stormwater was used in the pilot scale investigations because of the shortage of a long drought. Simulated stormwater was synthesized with various materials including road side sediment (SG = 2.0) to simulate suspended solids (SS) in stormwater. The particle sizes of sediment were less than 100 μm. After drying, these materials were fractionated according to particle size using a sieve and dilution with grit chamber wastewater to make simulated CSO with various SS concentrations. Graded materials were vigorously mixed with grit chamber wastewater and stored in a storage tank and mixed continuously using a mixer in order to obtain homogeneity. The influent and effluent samples were taken simultaneously and the SS was measured by weighing the retained GF/C filter mass after 2 h drying at 105 °C. A laser diffraction particle size analyzer (Shimadzu model SALD-2101) was used to determine the particle size and distribution. The measured particle size ranged from 0.03 to 1,000 μm and distributed into 50 intervals. The accumulated size percentage of solid, a number of particles, mean diameter based on volume, and 90% particle size (d90) were directly measured by this analyzer. To determine the removal efficiency for various influent SS concentrations and turbidity (NTU), a series of tests were performed. The range of surface loading rate for filtration was 453.6–528.0 m3/m2/day (mean 496.0 m3/m2/day), and the filtration retention time was 3.8–4.4 min (mean 4.1 min). The influent SS concentrations, turbidity were varied ranging from 118.0 to 366.0 mg/L (mean 238.8 mg/L), and 39.6 to 114.0 NTU (mean 76.2 NTU). During the experimental runs, the removal efficiency (%) was calculated by Equation (1).  
formula
(1)
where CI and Co are SS (mg/L) and turbidity (NTU) of influent and effluent.

RESULTS AND DISCUSSION

SFS operation without coagulant

The BHFF run without coagulant dosing had a total operation time of 14.8 h. More than six experiments were carried out with various conditions such as different SS concentrations. Results calculated in terms of SS and turbidity removal efficiency are shown in Table 2 and Figures 2 and 3. As shown Table 2, results showed that the range of SS and turbidity removal efficiency were 72.0–86.6% (mean 80.0%) and 30.9–71.1% (mean 49.3%), respectively. The variation of surface overflow rate (SOR), retention time, head loss, and SS solid loading rate were shown in Figure 3. When solid loading increased, SS removal efficiency rapidly decreased. The calculated average solid load was 12.4 kg/m2. There is no correlation between removal efficiency and head loss. A number of samples were analyzed for particle size distribution. The range of DMean for influent and effluent were 4.6–35.8 μm (mean 18.3 μm), 2.7–24.5 μm (mean 8.3 μm), respectively.

Table 2

Summary results operation condition and SS and turbidity removal efficiency without coagulants

Test no. Duration (hr) Range Flowrate (m3/day) Linear velocity (m/hr) Retention time (min) SOR (m3/m2·d) Influent
 
Effluent
 
SS load (kg/m2Head loss (mm) Turbidity removal (%) SS removal (%) 
Turbidity (NTU) SS (mg/L) Turbidity (NTU) SS (mg/L) 
1st 1.3 Min 18.9 18.9 3.8 453.6 76.2 200.0 30.4 38.0 – – 58.9 79.6 
Max 22.0 22.0 4.4 528.0 114.0 260.0 34.7 42.0 5.8 80.0 71.1 85.4 
Mean 20.6 20.6 4.1 494.4 90.3 226.8 32.4 40.3 – – 63.4 82.1 
2nd 1.3 Min 19.0 19.0 4.1 456.2 64.5 204.0 34.1 40.0 – – 38.6 79.6 
Max 20.7 20.7 4.4 495.6 82.1 246.0 41.0 46.0 5.0 73.0 55.4 83.2 
Mean 19.8 19.8 4.2 476.3 74.4 224.8 38.1 42.0 – – 48.4 81.2 
3rd 1.4 Min 19.4 19.4 3.9 465.6 39.6 118.0 20.1 28.0 – – 31.7 74.6 
Max 21.6 21.6 4.3 518.4 51.9 150.0 28.6 32.0 4.1 64.0 58.1 80.0 
Mean 20.7 20.7 4.1 496.3 44.6 133.8 23.7 29.6 – – 46.3 77.8 
4th 3.6 Min 19.7 19.7 3.9 472.8 63.2 200.0 35.0 40.0 – – 31.3 73.0 
Max 21.5 21.5 4.3 516.0 74.6 228.0 43.4 54.0 16.0 110.0 53.1 81.3 
Mean 20.7 20.7 4.1 495.7 69.2 216.0 39.3 46.1 – – 43.1 78.4 
5th 3.6 Min 20.1 20.1 3.9 482.4 70.5 222.0 34.6 42.0 – – 30.9 67.6 
Max 21.8 21.8 4.2 523.2 84.4 310.0 49.8 72.0 19.4 145.0 56.9 85.2 
Mean 21.0 21.0 4.0 502.9 78.0 260.8 41.9 52.8 – – 46.1 79.2 
6th 3.6 Min 20.2 20.2 3.9 484.8 85.2 286.0 37.7 46.0 – – 44.9 72.0 
Max 21.8 21.8 4.2 523.2 108.7 366.0 49.8 88.0 24.0 155.0 62.0 86.6 
Mean 20.9 20.9 4.0 500.9 93.5 315.3 43.4 58.9 – – 53.4 81.3 
Total 14.8 Min 18.9 18.9 3.8 453.6 39.6 118.0 20.1 28.0 4.1 64.0 30.9 72.0 
Max 22.0 22.0 4.4 528.0 114.0 366.0 49.8 88.0 24.0 155.0 71.1 86.6 
Mean 20.7 20.7 4.1 496.0 76.2 238.8 37.8 47.0 12.4 104.5 49.3 80.0 
Test no. Duration (hr) Range Flowrate (m3/day) Linear velocity (m/hr) Retention time (min) SOR (m3/m2·d) Influent
 
Effluent
 
SS load (kg/m2Head loss (mm) Turbidity removal (%) SS removal (%) 
Turbidity (NTU) SS (mg/L) Turbidity (NTU) SS (mg/L) 
1st 1.3 Min 18.9 18.9 3.8 453.6 76.2 200.0 30.4 38.0 – – 58.9 79.6 
Max 22.0 22.0 4.4 528.0 114.0 260.0 34.7 42.0 5.8 80.0 71.1 85.4 
Mean 20.6 20.6 4.1 494.4 90.3 226.8 32.4 40.3 – – 63.4 82.1 
2nd 1.3 Min 19.0 19.0 4.1 456.2 64.5 204.0 34.1 40.0 – – 38.6 79.6 
Max 20.7 20.7 4.4 495.6 82.1 246.0 41.0 46.0 5.0 73.0 55.4 83.2 
Mean 19.8 19.8 4.2 476.3 74.4 224.8 38.1 42.0 – – 48.4 81.2 
3rd 1.4 Min 19.4 19.4 3.9 465.6 39.6 118.0 20.1 28.0 – – 31.7 74.6 
Max 21.6 21.6 4.3 518.4 51.9 150.0 28.6 32.0 4.1 64.0 58.1 80.0 
Mean 20.7 20.7 4.1 496.3 44.6 133.8 23.7 29.6 – – 46.3 77.8 
4th 3.6 Min 19.7 19.7 3.9 472.8 63.2 200.0 35.0 40.0 – – 31.3 73.0 
Max 21.5 21.5 4.3 516.0 74.6 228.0 43.4 54.0 16.0 110.0 53.1 81.3 
Mean 20.7 20.7 4.1 495.7 69.2 216.0 39.3 46.1 – – 43.1 78.4 
5th 3.6 Min 20.1 20.1 3.9 482.4 70.5 222.0 34.6 42.0 – – 30.9 67.6 
Max 21.8 21.8 4.2 523.2 84.4 310.0 49.8 72.0 19.4 145.0 56.9 85.2 
Mean 21.0 21.0 4.0 502.9 78.0 260.8 41.9 52.8 – – 46.1 79.2 
6th 3.6 Min 20.2 20.2 3.9 484.8 85.2 286.0 37.7 46.0 – – 44.9 72.0 
Max 21.8 21.8 4.2 523.2 108.7 366.0 49.8 88.0 24.0 155.0 62.0 86.6 
Mean 20.9 20.9 4.0 500.9 93.5 315.3 43.4 58.9 – – 53.4 81.3 
Total 14.8 Min 18.9 18.9 3.8 453.6 39.6 118.0 20.1 28.0 4.1 64.0 30.9 72.0 
Max 22.0 22.0 4.4 528.0 114.0 366.0 49.8 88.0 24.0 155.0 71.1 86.6 
Mean 20.7 20.7 4.1 496.0 76.2 238.8 37.8 47.0 12.4 104.5 49.3 80.0 
Figure 2

The results of filtration pilot test in case of without hydrocyclone coagulation. (a) SS and (b) turbidity.

Figure 2

The results of filtration pilot test in case of without hydrocyclone coagulation. (a) SS and (b) turbidity.

Figure 3

The variation of surface overflow rate, head loss, SS solid loading rate in case of without hydrocyclone coagulation. (a) SOR and retention time; (b) head loss and SS loading.

Figure 3

The variation of surface overflow rate, head loss, SS solid loading rate in case of without hydrocyclone coagulation. (a) SOR and retention time; (b) head loss and SS loading.

Filter backwashing and solid mass balance in case of without coagulant use

To backwash a filter, the influent value is closed, and the whole wastewater is drained. After draining, the column is filled with effluent and first backwashing by blowing air for 3 min, and repeated twice in the same way. The SFS was backwashed by blowing air with effluent water through for 3 min at a rate of 60 m3/m2/h and after two backwashes, the whole drained wastewater was collected for mass balanced analysis. Six series of backwashing experiments were conducted to determine the effectiveness of air blowing. As the results of six series of the backwashing experiments and SS loading mass balance analysis, the recovery rate of filter was 79.2–83.6% (mean 81.2%) and the rate of remained solid loading in filter media was 16.4–20.8% (mean 18.8%) after backwashing.

SFS operation with coagulant

The SFS run with coagulant dosing had a total operation time of 4 h. Among the several types of coagulants, polyaluminium chloride silicate (PACS) was selected for stormwater treatment. As the results of the Jar test showed that PACS optimum dosage was 7.0 mg/L, these conditions left residual turbidity at less than 2.0 NTU. More than three experiments were carried out with various conditions such as different SS concentrations. The results calculated in terms of SS and turbidity removal efficiency are shown in Table 3 and Figure 4. The range of influent flow rate and surface overflow rate were 6.8–8.0 m3/day (mean 7.2 m3/day) and 163.2–191.8 m3/m2/day (mean 172.4 m3/m2/day), respectively. The influent turbidity, SS concentrations were 59.0–90.7 NTU (mean 72.0 NTU) and 194.0–320.0 mg/L (mean 246.7 mg/L), respectively. The range of PACS dosage concentration was 6.0–7.1 mg/L (mean 6.7 mg/L). As shown Table 3, the results showed that the range of SS and turbidity removal efficiency were 84.9–98.2 (mean 91.4%) and 70.7–96.3 (mean 84.0%), respectively. The variation of head loss, solid loading and SS removal efficiency were shown in Figure 5. The range of DMean for influent and effluent were 13.1–27.2 μm (mean 18.6 μm) and 14.3–31.9 μm (mean 22.0 μm), respectively.

Table 3

Summary results operation condition and SS and turbidity removal efficiency with coagulants

Test no. Duration (h) Range Flowrate (m3/day) Linear velocity (m/h) Retention time (min) SOR (m3/m2·d) PACS dosage (mg/L) Influent
 
Effluent
 
SS load (kg/m2Head loss (mm) Turbidity removal (%) SS removal (%) 
Turbidity (NTU) SS (mg/L) Turbidity (NTU) SS (mg/L) 
1st 3.0 Min 6.8 6.8 11.7 163.2 6.7 62.0 212.0 4.9 6.0 – – 70.7 85.8 
Max 7.2 7.2 12.4 172.8 7.1 73.0 274.0 20.3 32.0 5.3 60.0 92.9 97.6 
Mean 7.0 7.0 12.1 167.2 6.9 67.0 238.3 12.5 19.9 – – 81.2 91.5 
2nd 3.0 Min 6.9 6.9 11.4 165.6 6.5 59.0 194.0 2.6 4.0 – – 74.5 85.6 
Max 7.4 7.4 12.2 177.6 7.0 73.0 242.0 17.1 30.0 5.0 60.0 96.3 98.2 
Mean 7.2 7.2 11.8 171.6 6.7 66.7 215.6 10.7 19.1 – – 84.1 91.3 
3rd 3.0 Min 7.1 7.1 10.5 170.2 6.0 71.4 266.7 4.1 6.0 – – 78.9 85.9 
Max 8.0 8.0 11.8 191.8 6.8 90.7 320.0 16.2 38.0 6.4 70.0 95.4 98.1 
Mean 7.4 7.4 11.3 178.5 6.5 82.2 286.3 10.7 24.0 – – 86.8 91.5 
Total 9.0 Min 6.8 6.8 10.5 163.2 6.0 59.0 194.0 2.6 4.0 5.0 60.0 70.7 84.9 
Max 8.0 8.0 12.4 191.8 7.1 90.7 320.0 20.3 38.0 6.4 70.0 96.3 98.2 
Mean 7.2 7.2 11.7 172.4 6.7 72.0 246.7 11.3 21.0 5.6 63.3 84.0 91.4 
Test no. Duration (h) Range Flowrate (m3/day) Linear velocity (m/h) Retention time (min) SOR (m3/m2·d) PACS dosage (mg/L) Influent
 
Effluent
 
SS load (kg/m2Head loss (mm) Turbidity removal (%) SS removal (%) 
Turbidity (NTU) SS (mg/L) Turbidity (NTU) SS (mg/L) 
1st 3.0 Min 6.8 6.8 11.7 163.2 6.7 62.0 212.0 4.9 6.0 – – 70.7 85.8 
Max 7.2 7.2 12.4 172.8 7.1 73.0 274.0 20.3 32.0 5.3 60.0 92.9 97.6 
Mean 7.0 7.0 12.1 167.2 6.9 67.0 238.3 12.5 19.9 – – 81.2 91.5 
2nd 3.0 Min 6.9 6.9 11.4 165.6 6.5 59.0 194.0 2.6 4.0 – – 74.5 85.6 
Max 7.4 7.4 12.2 177.6 7.0 73.0 242.0 17.1 30.0 5.0 60.0 96.3 98.2 
Mean 7.2 7.2 11.8 171.6 6.7 66.7 215.6 10.7 19.1 – – 84.1 91.3 
3rd 3.0 Min 7.1 7.1 10.5 170.2 6.0 71.4 266.7 4.1 6.0 – – 78.9 85.9 
Max 8.0 8.0 11.8 191.8 6.8 90.7 320.0 16.2 38.0 6.4 70.0 95.4 98.1 
Mean 7.4 7.4 11.3 178.5 6.5 82.2 286.3 10.7 24.0 – – 86.8 91.5 
Total 9.0 Min 6.8 6.8 10.5 163.2 6.0 59.0 194.0 2.6 4.0 5.0 60.0 70.7 84.9 
Max 8.0 8.0 12.4 191.8 7.1 90.7 320.0 20.3 38.0 6.4 70.0 96.3 98.2 
Mean 7.2 7.2 11.7 172.4 6.7 72.0 246.7 11.3 21.0 5.6 63.3 84.0 91.4 
Figure 4

The results of filtration pilot test in case of with hydrocyclone coagulation. (a) SS; (b) turbidity.

Figure 4

The results of filtration pilot test in case of with hydrocyclone coagulation. (a) SS; (b) turbidity.

Figure 5

The variation of head loss, SS loading and removal efficiency in case of no hydrocyclone coagulation.

Figure 5

The variation of head loss, SS loading and removal efficiency in case of no hydrocyclone coagulation.

Filter backwashing and solid mass balance in case of with coagulant use

Backwashing begins when the drainage pipe valve at the filtration tank bottom is completely open (backwashing stage 1). Backwashing stage 2 was using air bubbles and water jet washing the media for 3 min and opening the drainage valve. After backwashing stage 2, SS loading 92.0–92.5% (mean 92.3%) was discharged from the filtration tank. Three series of backwashing experiments were conducted to determine the effectiveness of air blowing. The results of these three series of the backwashing experiments and SS loading mass balance analysis are summarized in Table 4. The recovery rate of filter was 92.0–92.5% (mean 92.3%) the rate of remaining solid loading in the filter media was 6.1–8.2% (mean 7.2%) after backwashing. Figure 6 shows the accumulated floc formation inside the filter media.

Table 4

The results of three series of the backwashing experiments

Process Item Unit Combined sewer overflows (CSOs)
 
1st 2nd 3rd 
Influent m3/h 7.0 7.2 7.4 
Operation time 3.0 3.0 3.0 
SS mg/L 238.3 215.6 286.3 
kg 5.0 4.6 6.4 
SSIn 100.0 100.0 100.0 
Pilot plant Volume m3 1.4 1.4 1.4 
Retention time min 12.1 11.7 11.3 
Filtration area m2 1.0 1.0 1.0 
Linear velocity m/h 7.0 7.2 7.4 
SS load kg/m2 5.0 4.6 6.4 
PACS mg/L 167.2 171.6 178.5 
SOR m3/m2·day 6.9 6.7 6.5 
Head loss mm 60.0 60.0 70.0 
Residual SS kg 0.4 0.3 0.5 
8.2 6.1 7.3 
Backwash stagnant water Air Q m3/h 10.0 10.0 10.0 
Air time min 5.0 5.0 5.0 
Air volume m3 0.8 0.8 0.8 
Air injection rate m3/m2·h 10.0 10.0 10.0 
Volume m3 1.9 1.9 1.9 
SS mg/L 1,530.0 1,350.0 2,110.0 
kg 2.9 2.6 4.0 
SSBW1/SSIn 58.4 55.5 62.8 
Backwash effluent Air Q m3/h 10.0 10.0 10.0 
Air time min 5.0 5.0 5.0 
Air volume m3 0.8 0.8 0.8 
Air injection rate m3/m2·h 10.0 10.0 10.0 
Volume m3 1.9 1.9 1.9 
SS mg/L 680.0 740.0 750.0 
kg 1.3 1.4 1.4 
SSBW2/SSIn 25.9 30.4 22.3 
Effluent Volume m3 18.9 19.4 20.3 
SS mg/L 19.9 19.1 24.0 
kg 0.4 0.4 0.5 
SSOut/SSIn 7.5 8.0 7.6 
SS removal efficiency 92.5 92.0 92.4 
Process Item Unit Combined sewer overflows (CSOs)
 
1st 2nd 3rd 
Influent m3/h 7.0 7.2 7.4 
Operation time 3.0 3.0 3.0 
SS mg/L 238.3 215.6 286.3 
kg 5.0 4.6 6.4 
SSIn 100.0 100.0 100.0 
Pilot plant Volume m3 1.4 1.4 1.4 
Retention time min 12.1 11.7 11.3 
Filtration area m2 1.0 1.0 1.0 
Linear velocity m/h 7.0 7.2 7.4 
SS load kg/m2 5.0 4.6 6.4 
PACS mg/L 167.2 171.6 178.5 
SOR m3/m2·day 6.9 6.7 6.5 
Head loss mm 60.0 60.0 70.0 
Residual SS kg 0.4 0.3 0.5 
8.2 6.1 7.3 
Backwash stagnant water Air Q m3/h 10.0 10.0 10.0 
Air time min 5.0 5.0 5.0 
Air volume m3 0.8 0.8 0.8 
Air injection rate m3/m2·h 10.0 10.0 10.0 
Volume m3 1.9 1.9 1.9 
SS mg/L 1,530.0 1,350.0 2,110.0 
kg 2.9 2.6 4.0 
SSBW1/SSIn 58.4 55.5 62.8 
Backwash effluent Air Q m3/h 10.0 10.0 10.0 
Air time min 5.0 5.0 5.0 
Air volume m3 0.8 0.8 0.8 
Air injection rate m3/m2·h 10.0 10.0 10.0 
Volume m3 1.9 1.9 1.9 
SS mg/L 680.0 740.0 750.0 
kg 1.3 1.4 1.4 
SSBW2/SSIn 25.9 30.4 22.3 
Effluent Volume m3 18.9 19.4 20.3 
SS mg/L 19.9 19.1 24.0 
kg 0.4 0.4 0.5 
SSOut/SSIn 7.5 8.0 7.6 
SS removal efficiency 92.5 92.0 92.4 
Figure 6

The accumulated floc formation inside filter media.

Figure 6

The accumulated floc formation inside filter media.

CONCLUSIONS

This study has been carried out to evaluate the applicability of the hybrid type of stormwater runoff treatment system (SFS) and determine the optimum operational parameter such as coagulation dosage concentration, with or without coagulants, surface loading rate and backwashing conditions. The SFS consists of hydrocyclone coagulation/flocculation with polyaluminium chloride silicate (PACS) and upflow filter to treat combined sewer overflows. There are two modes (without PACS use and with PACS use) of operation for the SFS. In case of no coagulant use, the range of SS and turbidity removal efficiency was 72.0–86.6% (mean 80.0%) and 30.9–71.1% (mean 49.3%), respectively. And, the recovery rate of the filter was 79.2–83.6% (mean 81.2%) and the rate of remaining solid loading in the filter media was 16.4–20.8% (mean 18.8%) after backwashing. The results of Jar test showed that PACS optimum dosage was 7.0 mg/L; these conditions left residual turbidity to less than 2.0 NTU. In the case of SFS run with coagulant use, the range of influent flow rate and surface overflow rate were 6.8–8.0 m3/day (mean 7.2 m3/day) and 163.2–191.8 m3/m2/day (mean 172.4 m3/m2/day), respectively. The influent turbidity and SS concentrations were 59.0–90.7 NTU (mean 72.0 NTU) and 194.0–320.0 mg/L (mean 246.7 mg/L), respectively. The range of PACS dosage concentration was 6.0–7.1 mg/L (mean 6.7 mg/L). The range of SS and turbidity removal efficiency was 84.9–98.2 (mean 91.4%) and 70.7–96.3 (mean 84.0%), respectively. It was found that removal efficiency was enhanced with PACS dosage. The recovery rate of filter was 92.0–92.5% (mean 92.3%) and the rate of remaining solid loading in filter media was 6.1–8.2% (mean 7.2%) after backwashing. In case of coagulant use, the particle size of the effluent is bigger than influent particle size. The results showed that SFS with PACS use is more effective than without PACS use in SS and turbidity removal efficiency and recovery rate of filter. The SFS, which came out to solve the problems of low efficiency of removing microparticles of upflow filtration type stormwater treatment devices, is considered as an alternative system.

ACKNOWLEDGEMENTS

This study was funded by a grant from the National Research Foundation of Korea (NRF-2017 R1D1A1B03033724) and the Korea National University of Transportation in 2018. Their continuing support for this research is greatly appreciated.

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