https://orcid.org/0000-0001-7239-7631
ABSTRACT
The performance of a combined up-flow submerged aerated biological filter (SABF) and photocatalytic process (PC) for the treatment of grey water was studied. The removal of COD, hardness, alkalinity, and turbidity was considered. The removal efficiency of SABF using organic and inorganic packing materials was evaluated. The combined SABF and PC removed 100% of COD, up to an organic loading rate (OLR) of 0.21 ± 0.05 kg/m3/day at 12 h HRT, irrespective of the packing media. The fibrous outer shell of coconut fibres favoured turbidity removal, but both the organic and inorganic packing materials showed equal performance in the removal of physicochemical parameters of the grey water.
HIGHLIGHTS
Comparison of organic and inorganic packing materials for the grey water treatment in aerobic biofilter.
Secondary treatment of grey water using the photocatalytic process.
Achieved 100% COD, alkalinity, and turbidity removal.
75% of hardness removal achieved.
INTRODUCTION
The potential for the reuse of treated grey water is gaining importance due to water stress. The average percentage of grey water generation represents 50–80% of total water use. The grey water with a comparatively less pollution load can be reused in various applications like toilet flushing, gardening, etc., after an appropriate treatment. Several contaminants like suspended and dissolved solids, oil and grease, heavy metals, chemicals, and pathogens are reported in grey water (Friedler 2004). The organic fraction is 30%, whereas the nutrient content is about 9–20% (Roeleveld & Zeeman 2006). Several treatment options exist to treat grey water. More reports include a combination of sand filtration followed by a biological process. The sand filter with several combinations of stones, gravel, natural mulch (Ludwig 2000), activated carbon (Noutsopoulos et al. 2018) along with several locally available materials such as peat and charcoal, (Wurochekke et al. 2016) has been used for grey water treatment. The combination of sand filters along with the zeolites increased the removal of ammonium, phosphates, and nitrates from grey water and are dependent on the operating parameters (Widiastuti et al. 2011; Assayed et al. 2014). Among the biological systems, anaerobic treatment is not recommended due to the low reduction of COD (Li et al. 2010). The potential of aerobic treatment systems such as sequential batch reactors, rotating biological contactors, and MBRs (Anjoo Anna & Sheela 2010; Ashfaq et al. 2011; Ding et al. 2017; Khondabi et al. 2018) were explored by several researchers. Limited studies also explore the potential of the constructed wetlands (CWs; Pachkor & Parbat 2017) and vermifiltration (Parul & Tanaya 2020) as a treatment option for the urban areas. Hence, there is a need for the development of a suitable cost-effective and eco-friendly hybrid treatment method to overcome the problems encountered in the current treatment systems.
In the present study, an attempt has been made to study the performance of a hybrid treatment system including a submerged aerated biological filter (SABF) and photocatalytic system. SABF systems are very much efficient in the treatment of different organic loadings including VOCs in wastewater (Priya & Philip 2015), 91.2% for landfill leachate (Galvez et al. 2006), 98% for atrazine (Baghapour et al. 2013), 51% for amoxicillin (Baghapour et al. 2014), 90% removal for water-borne volatile organic compounds (Cheng 2009), 86% removal for oil-field produced water (Delin et al. 2007), 92% removal for textile wastewater (Chang et al. 2002), and 85% removal for municipal wastewater (Liu et al. 2010) and there are seldom any reports on the treatment of grey water using SABF.
Barzegar et al. (2019) studied the treatment of grey water using an electrocoagulation (EC)/ozone process and reported 95 and 87% removal COD and TOC, respectively. Among different chemical treatment methods adopted for the treatment of grey water, photocatalysis has shown better efficiency during the treatment of grey water from hotels with 100% removal of anionic surfactants, personal care products, and laundry detergents with TiO2 as a catalyst (Sanchez et al. 2010). Priyanka et al. (2020) also reported 93.1% of total organic carbon and 98.5% of benzophenone during the treatment of real-time grey water by modified TiO2 (G-NP-TiO2) under solar illumination.
In SABF, the selection of packing media is one of the factors influencing the performance of the SABF. When compared with conventional synthetic media, pollutant removal is reported to be comparatively good when using natural materials as packing media (Moore et al. 1999). Various natural packing media such as lava stones (Martínez et al. 2007), natural zeolite with sand as media (Chang et al. 2002), oyster shell (Liu et al. 2010), and volcanic scoria (Sagastume & Noyola 2008) were explored and the performance of such packing media was highly influenced by its properties such as media type (floating or sunken) surface area, size, and shape (Hassimi et al. 2009). It has also been reported that natural fibrous material such as sisal and oil palm empty fruit bunch (OPEFB) fibres has contributed to 69.5% of COD removal during the treatment of municipal wastewater because of its high surface area (Vinod & Mahalingegowda 2012). The use of natural materials would make this treatment system an even more sustainable treatment option.
The main objective of the study is to (i) assess the performance of SABF individually using two different packing mediums in the SABF, such as coconut fibre and fujino spiral and (ii) assess the effectiveness of photocatalysis in the visible range as a polishing treatment. The photocatalytic process has the potential to mineralise complex contaminants into simple and non-toxic compounds such as CO2 and H2O without generating secondary pollutants (Marwah et al. 2022; Mishra et al. 2023). Ce3+/TiO2 photocatalyst was found to be more stable than TiO2 (Bharatvaj et al. 2018), and hence, in this study, Ce3+/TiO2 is used as a photocatalyst to treat grey water.
MATERIALS AND METHODS
Materials
Grey water
The apartment has seven multi-story buildings with 15 floors each and a total of 525 houses. The grey water was collected from the grey water collection sump at 8 a.m. regularly. The majority of the grey water contains kitchen grey water.
Microorganism and culture media
The return sludge from the secondary clarifier of the activated sludge process from the domestic sewage treatment plant at Vaniyambaadi, Vellore, India, was used in the SABF.
Packing media
In the present study, for the attachment of the bacteria in the SABF, two packing media were used, and their performance with respect to grey water treatment was assessed individually. The media used are (i) spirals supplied by Fujino spirals, India and (ii) coconut fibre. The spirals are made of polyvinyl chloride (PVC). The average size of the spirals was 40 mm, with a surface area of approximately 350 m2/m3. The specific gravity and density of the packing media were 1.05 and 110 g/L, respectively. The amount of coconut fibre used as packing material in SABF was 1.126 kg, and the density of this packing bed was found to be 72 kg/m3.
Experimental set-up for SABF and photocatalytic reactor
Experimental set-up for SABF and photocatalytic reactor. 1 – Inlet chamber, 2 – Inlet pump, 3 – Air pump, 4 – Drain pipe, 5 – Inlet pipe, 6 – Perforated pipe for air supply, 7 – Submerged aerated biological filter (filled with packing media – Fujino spiral/Coconut fibre), 8 – Outlet pipe, 9 – Wooden chamber, 10 – Light source, 11 – Photocatalytic chamber (5 L capacity), 12 – inlet pipe for photocatalytic chamber, 13 – Outlet pipe for photocatalytic chamber.
Experimental set-up for SABF and photocatalytic reactor. 1 – Inlet chamber, 2 – Inlet pump, 3 – Air pump, 4 – Drain pipe, 5 – Inlet pipe, 6 – Perforated pipe for air supply, 7 – Submerged aerated biological filter (filled with packing media – Fujino spiral/Coconut fibre), 8 – Outlet pipe, 9 – Wooden chamber, 10 – Light source, 11 – Photocatalytic chamber (5 L capacity), 12 – inlet pipe for photocatalytic chamber, 13 – Outlet pipe for photocatalytic chamber.
Mechanism of grey water treatment using the photocatalytic process.
Synthesis of Ce3+–TiO2
Ce3+–TiO2 was synthesised by a sol-gel method (Bharatvaj et al. 2018).
Experimental set-up for the photocatalytic reactor
Photographic view of combined SABF and photocatalytic reactor.
Experimental studies
In the present biodegradation study, the performance of SABF was assessed for two different packing materials individually. During the start-up, the packed media (coconut fibre) was filled inside the reactor to favour the early attachment of biomass. Initially, the empty weight of the SABF reactor with the packing material was noted (W1). The submerged, aerated biological filter was inoculated for 24 h with the activated sludge. After draining, the SABF reactor weight along with the biomass was noted (W2). Then, the grey water was allowed to pass through the SABF for treatment. The rate of flow of grey water was 25 mL/min. On a daily basis, grey water was collected from the outlet of the SABF system. The inlet and outlet characteristics of the grey water were analysed, and the OLR of 0.21 ± 0.05 kg/m3/day at 12 h HRT was maintained. The treated grey water from the SABF system was then allowed to enter the photocatalytic system for further treatment. The final weight of the reactor was noted (W3). The treated grey water from the photocatalytic system was also collected on a daily basis to analyse the quality of the grey water before and after the treatment. The Ce3+/TiO2 photocatalyst of 0.2 g/L was used, and visible light radiation with three halogen lamps (47 W/m2 each) was used. A similar methodology was followed for fujino spiral packing material in order to study the biodegradation of grey water. The operational history is given in Table 1.
Degradation of COD using SABF and photocatalysis
| Grey water before treatment | Submerged aerated biological filter (SABF) | Photocatalytic reactor (PR) | ||||
|---|---|---|---|---|---|---|
| S. No. | Days | Inlet grey water COD | Packing material | COD Concentration after treatment | COD Concentration after treatment | Source of illumination |
| 1 | 1–10 | 64 mg/L | Fujino spiral | 20 mg/L | 0 mg/L (100%) | Visible light (147 W/m2) |
| 2 | 1–10 | 75 mg/L | Coconut fibre | 28 mg/L | 0 mg/L (100%) | |
| Grey water before treatment | Submerged aerated biological filter (SABF) | Photocatalytic reactor (PR) | ||||
|---|---|---|---|---|---|---|
| S. No. | Days | Inlet grey water COD | Packing material | COD Concentration after treatment | COD Concentration after treatment | Source of illumination |
| 1 | 1–10 | 64 mg/L | Fujino spiral | 20 mg/L | 0 mg/L (100%) | Visible light (147 W/m2) |
| 2 | 1–10 | 75 mg/L | Coconut fibre | 28 mg/L | 0 mg/L (100%) | |
Analytical procedure
The inlet and outlet liquid samples from both reactors were filtered through a 0.45 μm pore size filter paper (Whatman, USA) and analysed for soluble COD, hardness, alkalinity, and dissolved oxygen as per the standard methods for the examination of water and wastewater. pH was monitored by the pH meter, and turbidity was measured by the turbidity meter (InfraMake). The standard method was used for the examination of water and wastewater (APHA 2005).
RESULTS AND DISCUSSION
Hybrid treatment of grey water using SABF (coconut fibre) and photocatalysis
Grey water before and after the treatment using SABF (coconut fibre) and photocatalysis.
Grey water before and after the treatment using SABF (coconut fibre) and photocatalysis.
Mechanism of treatment using SABF (coconut fibre) and photocatalysis
In the current study, coconut fibres served as a good packing medium by favouring an enhanced bacterial attachment in their structure. The natural media, by their nature, possess a higher surface area (Vinod & Mahalingegowda 2012) and favour a higher contact between the media and the grey water. The smaller pores within the coconut fibres facilitated the formation of smaller settling zones, thereby resulting in the settling of the suspended particles and reducing the turbidity in the treated water. A considerable reduction in hardness was also observed, and this can be attributed to the extracellular polymeric substance generated by the bacteria, which is characterised by the presence of negatively charged functional groups and has the ability to absorb certain salts in the wastewater. The easy flow of air through such media resulted in the bacterial degradation of the organic content in the grey water.
Hybrid treatment of grey water using SABF (fujino spiral) and photocatalysis
During the start-up phase of the study, the circulation of activated sludge in the closed loop enhanced the bacterial attachment in the fujino spiral, which was used as a packing medium in the SABF. The sludge was drained after 24 h, and the grey water with an influent COD varying between 60 and 75 mg/L was fed into the SABF reactor. The treated water was collected from the outlet pipe, and parameters such as pH, turbidity, alkalinity, hardness, and COD were analysed. The effluent from SABF was further treated in a photocatalytic chamber, and the treated effluent was analysed for the parameters mentioned above.
Grey water before and after the treatment using SABF (fujino spiral) and photocatalysis.
Grey water before and after the treatment using SABF (fujino spiral) and photocatalysis.
Mechanism of treatment using SABF (fujino spiral) and photocatalysis
In this study, it was observed that dense microbial formation was observed in the fujino spiral. These biofilms serve as a matrix, thereby allowing the capture of suspended solids and also favouring the bacterial degradation of the organic pollutants in the wastewater.
Grey water treatment is one of the best ways to overcome water scarcity. Various treatment methods were reported for grey water treatment. Table 2 shows the review of chemical and biological treatment methods for grey water treatment.
Comparison of efficiency of treatment of chemical and biological methods with current research
| S. No. | Author name and year | Treatment method adopted | Percentage of degradation |
|---|---|---|---|
| 1. | Winward et al. (2008) | Chlorine disinfection | COD – 84% BOD – 82% TSS – 74% |
| 2. | Barzegar et al. (2019) | Electrocoagulation and ozonation/UV | COD – 88% BOD – 80% TOC – 78% TDS – 85.71% pH – 8.0 |
| 3. | Chin et al. (2009) | UVC/H2O2 | Turbidity – 31% pH – 1 COD – 87% |
| 4. | Sophia et al. (2017) | TiO2 photocatalysis/H2O2/Fe3+ | DOC – 72% |
| 5. | Priyanka et al. (2020) | TiO2 photocatalysis | TOC – 94% TKN – 50% |
| 6. | Sanchez et al. (2010) | TiO2 photocatalysis | DOC – 65% |
| 7. | Palmarin & Young (2019) | Hybrid membrane bioreactor (HMBR) | COD – 91% BOD – 97% TN – 74% Ammonia – 93% Phosphorous – 90% |
| 8. | Khuntia et al. (2019) | Aerobic bioreactor with macropore mesh filters (MF) | Removal of COD (a) Vertical * 50 μm MF – 88% * 100 μm MF – 91% (b) Horizontal * 50 μm MF – 83% * 100 μm MF – 90% |
| 9. | Lamine et al. (2007) | Sequencing batch reactor (SBR) | TSS – 76%, COD – 83%, BOD – 79%, TOC – 71%, NH4-N – 78% |
| 10. | Amr (2013) | Rotating biological contractors' systems (RBCs) | TSS – 94.8%, BOD – 95.9%, TKN – 74.3% |
| 11. | Sonali (2018) | Rotating biological contractors | pH – 7.3 Turbidity – 67% TSS – 68% BOD – 76% COD – 85% |
| 12. | Laaftet et al. (2015) | Horizontal subsurface flow constructed wetland (HFSSCW) | Turbidity – 88% TSS – 90% BOD5 – 87% COD – 89% TN – 42% TP – 50% |
| 13. | Lamine et al. (2012) | Submerged membrane bioreactor with gravitational filtration | SS – 52% COD – 99% BOD – 95% NH4-N – 80% NO3-N – 75% |
| 14. | Current research work | Combined SABF and PR | Turbidity – 100% Alkalinity – 100% COD – 100% Hardness – 75% |
| S. No. | Author name and year | Treatment method adopted | Percentage of degradation |
|---|---|---|---|
| 1. | Winward et al. (2008) | Chlorine disinfection | COD – 84% BOD – 82% TSS – 74% |
| 2. | Barzegar et al. (2019) | Electrocoagulation and ozonation/UV | COD – 88% BOD – 80% TOC – 78% TDS – 85.71% pH – 8.0 |
| 3. | Chin et al. (2009) | UVC/H2O2 | Turbidity – 31% pH – 1 COD – 87% |
| 4. | Sophia et al. (2017) | TiO2 photocatalysis/H2O2/Fe3+ | DOC – 72% |
| 5. | Priyanka et al. (2020) | TiO2 photocatalysis | TOC – 94% TKN – 50% |
| 6. | Sanchez et al. (2010) | TiO2 photocatalysis | DOC – 65% |
| 7. | Palmarin & Young (2019) | Hybrid membrane bioreactor (HMBR) | COD – 91% BOD – 97% TN – 74% Ammonia – 93% Phosphorous – 90% |
| 8. | Khuntia et al. (2019) | Aerobic bioreactor with macropore mesh filters (MF) | Removal of COD (a) Vertical * 50 μm MF – 88% * 100 μm MF – 91% (b) Horizontal * 50 μm MF – 83% * 100 μm MF – 90% |
| 9. | Lamine et al. (2007) | Sequencing batch reactor (SBR) | TSS – 76%, COD – 83%, BOD – 79%, TOC – 71%, NH4-N – 78% |
| 10. | Amr (2013) | Rotating biological contractors' systems (RBCs) | TSS – 94.8%, BOD – 95.9%, TKN – 74.3% |
| 11. | Sonali (2018) | Rotating biological contractors | pH – 7.3 Turbidity – 67% TSS – 68% BOD – 76% COD – 85% |
| 12. | Laaftet et al. (2015) | Horizontal subsurface flow constructed wetland (HFSSCW) | Turbidity – 88% TSS – 90% BOD5 – 87% COD – 89% TN – 42% TP – 50% |
| 13. | Lamine et al. (2012) | Submerged membrane bioreactor with gravitational filtration | SS – 52% COD – 99% BOD – 95% NH4-N – 80% NO3-N – 75% |
| 14. | Current research work | Combined SABF and PR | Turbidity – 100% Alkalinity – 100% COD – 100% Hardness – 75% |
From the above review on treatment methods for chemical grey water treatment, the common methods are chlorine disinfection, EC, and ozonation combined with UV and UVC/H2O2. Barzegar et al. (2019) reported EC/ozonation/UV photocatalysis, in which maximum degradation of grey water has been observed. Among the chemical methods used, the photocatalytic process shows a better efficiency of 75–95%. Hence, in this present study, the photocatalytic process is in the visible range along with the biological treatment method. The common methods used for biological grey water treatment are membrane bioreactors (MBRs), sequencing bioreactors (SBRs), aerobic bioreactors (ABRs), rotating biological contractors (RBCs), and CWs. Among these biological processes, the membrane bioreactor gives the maximum degradation of grey water. Lamine et al. (2012) reported that high-conventional MBRs show maximum reductions in different parameters like COD, BOD, etc. However, MBRs have drawbacks such as sudden clogging and fouling, high cost, non-portability, and time consumption. Next to MBR, the aerobic bioreactor shows a maximum degradation of 75–99%. Hence, in this present study, a submerged aerobic bioreactor with a novel packing material, coconut fibre, was used for the treatment of grey water. In the current research, the best chemical and biological treatment methods opted for grey water treatment was a submerged aerobic biofilter along with photocatalysis and achieved maximum efficiency of 100% for COD, turbidity, and alkalinity.
CONCLUSION
In the present study, it is very evident that the treatment efficiency that was obtained by placing a fujino spiral as attachment media was equally achievable while using natural coconut fibre. Hence, a considerable reduction of turbidity up to less than 1 NTU was achievable when compared with the fujino spiral. However, combined treatment of SABF and photocatalysis shows 100% COD, alkalinity, and turbidity removal, irrespective of the packing media. This indicates that both packing media favour a good retention of bacteria within the SABF system, thereby enhancing the removal of COD with higher efficiency. Both organic and inorganic packing materials show more or less equal performance with respect to the removal of alkalinity and hardness. However, the hardness removal achieved was 87%. This hardness can be further removed using membrane filtration, and the same water can be used for drinking or domestic purposes. Since the removal efficiency is high, the same treatment can be scaled up in the future for the benefit of society.
DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.
CONFLICT OF INTEREST
The authors declare there is no conflict.
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