Abstract

Food waste has been a complex component added to municipal solid waste, making it a major reason for the evolution of greenhouse gases, foul odour and a dwelling habitat for insects and microbes. Diversion of the mixed food waste (unsegregated) to useful materials (activated carbon) would have immense industrial significance. In this study, rice, vegetables, oil and spice (WCVR); mixed fruit peels including banana peel, pomegranate peel, orange peel and lemon peel (MFPW); plain rice (WCR) and mixed food waste (rice, dhal, vegetables, fruits, meat and bones) (MFW) were used. Food waste samples were heated at a temperature of 350 °C for 3 h in an incinerator and then activated with zinc chloride for 2 h in a muffle furnace maintained at 500–600 °C temperature. Zinc chloride activated carbon was characterized through X-ray diffraction, field emission scanning electron microscopy and fourier transform infrared spectroscopy. WCR carbon was the best-activated carbon, yielding nanomaterials with 2θ = 25.81, 31.76, 34.41 and 56.54, which was in accordance with the JCPDS card number. The MFW activated carbon reduced the biodiesel wash water pH from 10 to 6.5 making it suitable for recycling. Turbidity was reduced by 98.41%, chemical oxygen demand by 41.33%, oil and grease by 99.05% for MFW carbon.

HIGHLIGHTS

  • Biodiesel washwater was generated enormously during biodiesel synthesis.

  • Food waste was converted to activated carbon (AC) and activated with zinc chloride.

  • Synthesized AC had high intensity peaks at 31.9°, 34.5° and 36.5°.

  • 0.5 g AC reduced turbidity, COD, oil and grease by 98.41, 41.33 and 99.05%.

Graphical Abstract

Graphical Abstract
Graphical Abstract

INTRODUCTION

Food waste generation was around 1.4 billion tons per year in developing countries (Girotto et al. 2015; Kosheleva et al. 2019; Tucho & Okoth 2020). This may be attributed to the lack of awareness of the value of food, food security, poverty and societal wellbeing. Food waste when mixed with municipal solid waste results in stale odours from the waste dump yards contributing to secondary pollution. Food waste is rich in carbon-based materials, which can be processed through appropriate techniques for value-added products recovery (Joshi 2002; Pandey et al. 2016). Many investigators have processed food waste through anaerobic digestion to synthesize biogas (CO2, CH4), a green fuel for rural livelihoods (Cho et al. 1995). Although biogas production is the most popular utility for food waste, excess availability of food waste, lack of popularization of biogas application as a replacement to conventional cooking fuels and need for location-specific biogas plant installations in proximity to where the food waste is generated, needs private interest and remains a challenge that has led to the idea of developing a mechanism to divert a percentage of food waste to activated carbon. In larger communities (apartments, hostels, mansions, industries, etc), the food waste can be reduced through connected home techniques via smart mobile applications by providing ideas towards inventory management and cooking skills (Tavill 2020).

Food waste is converted to activated carbon via pyrolysis, hydrothermal carbonization, etc. This has emerged as a hot topic in the current scenario among environmental researchers working on industrial wastewater remediation. Food waste-based activated carbon possesses numerous advantages like less cost, enormous resource availability, etc. The best activated agent for the potential of activated carbon produced to adsorb various adsorbates from aqueous solutions are electrocoagulation (Chavalparit & Ongwandee 2009), coagulation, adsorption (Pitakpoolsil & Hunsom 2013), biological processes and microbial fuel cell systems. Adsorption is one of the most effective methods used for the treatment of wastewater from different sources (Halim et al. 2012; Bashir et al. 2015; Azmi et al. 2016). The use of activated carbon (AC) as an adsorbent was considered as one of the most efficient technologies for the removal of colorants, organic pollutants, chemical oxygen demand (COD), and heavy metals (Li et al. 2009). Activated carbon is highly porous in nature and has a wide range of practical applications because of its versatile adsorption capacity (Dabwan et al. 2015). Researchers around the globe have utilized bamboo, peach stones, grass, wood, agricultural wastes like coir pith, peanut hull, rice husk, palm trees, palm stones, fruit peel, sugar beet pulp, grain sorghum, wheat husk and industrial wastes for the synthesis of activated carbon (Yalcın & Sevinc 2000; Ramakrishnan & Namasivayam 2009; Abdul-Hameed & Al-Juboury 2020a, 2020b).

Activated carbon (AC) from materials has been preferably synthesized by chemical (Kumar & Jena 2016; Tran et al. 2018) or physical methods over recent years (Guan et al. 2013; Enaime et al. 2017). Chemical activation of carbonaceous material with ZnCl2 has resulted in 70% of adsorption capacity compared with activated carbon produced using other agents (Mahamad et al. 2015). Surface and structural analyses of activated carbon is the most important and essential property to be analyzed to decide its commercial applications (Dizbay-Onat et al. 2018; Inbaraj et al. 2021). Several researchers have attempted to use homogeneous food waste generated from processing raw materials, to be diverted for activated carbon synthesis (Dhandapani et al. 2020; Yang et al. 2021). This reported study was taken up to investigate the effect of four different food waste samples generated routinely into ZnCl2 incorporated activated carbon for the treatment of biodiesel wash water, to evaluate its efficiency for the removal of turbidity and reduction of pH.

Water scarcity and treatment regimes in various sectors including biodiesel production, dying industries, electroplating, etc., are emerging from research around the globe (Baldev et al. 2018; MubarakAli 2019). Transesterification processes generate a huge amount of wash water (wastewater) during the biodiesel production owing to the wet washing step (Chung et al. 2019; Poornapushpakala et al. 2021). Biodiesel wash water will be alkaline in nature with pH above 9 (Mustafa & Asmatulu 2020). Wash water reuse will reduce the dependence of biodiesel industries on freshwater resources and will decrease the amount spent on freshwater requirements during wet washing.

The study was extended further to synthesize a heterogeneous food waste ZnCl2 activated carbon, to eliminate the process of segregation of food waste into homogeneous food waste samples, thereby reducing the investment of time and money on segregation. Food waste activated carbon is reported as a novel adsorbent efficient in treating highly turbid, strongly alkaline wastewater including biodiesel wash water. Also, this will be a first-time attempted mechanism in which mixed food waste (MFW) of maximum heterogeneity generated, can be diverted indigenously towards activated carbon synthesis, contributing to a sustainable approach for recycling food waste which would otherwise become an added source of organic pollution when dumped on landfills.

Figure 1

XRD patterns of carbonaceous food waste samples before activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 1

XRD patterns of carbonaceous food waste samples before activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 2

XRDs pattern of carbonaceous food waste samples after activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 2

XRDs pattern of carbonaceous food waste samples after activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 3

FESEM images of food waste samples before ZnCl2 activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 3

FESEM images of food waste samples before ZnCl2 activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 4

FESEM images of food waste samples after ZnCl2 activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 4

FESEM images of food waste samples after ZnCl2 activation of WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 5

FTIR spectra of raw WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 5

FTIR spectra of raw WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 6

FTIR spectra of ZnCl2 activated WCVR (a), MFPW (b), WCR (c) and MFW (d).

Figure 6

FTIR spectra of ZnCl2 activated WCVR (a), MFPW (b), WCR (c) and MFW (d).

EXPERIMENTAL METHODS

Materials and chemicals

Food waste was collected from the Sathyabama Institute of Science and Technology Chennai, Tamil Nadu, India that has a mess hall, catering to about 12,000 people every day and hence is identified as a potential source for food waste collection. Zinc chloride (ZnCl2) with purity >98% was purchased from Fisher Scientific Mumbai and an incinerator (model A1500 150* 100 * 96 cm Italy) was used.

Collection of food waste and analysis

Four different food wastes namely rice, vegetables, oil and spice (WCVR); mixed fruit peels including banana peel, pomegranate peel, orange peel and lemon peel (MFPW); plain rice (WCR) and mixed food waste containing rice, dhal, vegetables, fruits, meat and bones (MFW) were collected in plastic buckets and subjected to proximate studies as per ASTM International D3,173–3,175 test standards.

Preparation of activated carbon from food waste

The collected food waste samples were dried for 8 h in sunlight to remove moisture and subsequently oven dried at 105 °C for 4–5 h to remove remaining bound moisture. The waste samples were heated at 350 °C for a time of 3 h in an incinerator (model A1500 150* 100 * 96 cm Italy) to convert the dried food waste into carbon. Furthermore, the dried carbonaceous food waste samples were size reduced using a ball mill (SPEX 8000M-230 dual mixer mill, 230 V/50 Hz USA) for 15 min and sieved through a 40-mesh screen. The synthesized carbon powder was doped in 1 N ZnCl2 solution in the ratio 1 g:2 mL for 2 h at 80 °C (Saqib et al. 2018). The ZnCl2-doped carbon samples were further activated at 500–600 °C in a muffle furnace for 2 h. The activated samples were size reduced with a pestle and mortar to produce fine activated carbon. The activated carbon samples were then washed with distilled water to reduce the pH to neutral. The washed activated carbon samples were dried in a hot air oven at 110 °C for 2 h and crushed to produce the activated carbon. The procedure was carried out for all four food waste samples collected.

Characterization of food waste carbon

The ZnCl2 activated carbon samples obtained from food waste samples WCVR, MFPW, WCR and MFW were characterized for their crystalline or amorphous nature, surface morphology and presence of functional groups using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform-infrared spectroscopy studies. The XRD technique was used to examine the crystalline and non-crystalline nature of the material. XRD was performed using an analytical D/Max-2500 X-ray diffractometer equipped with Cu-Kα radiation (1.5406 Å) operating at 40 kV, 50 mA in the 2θ range of 20°–80° with scanning rate of 0.02 S−1. Thus, phase analysis and the nature of activated carbon were confirmed using XRD. FESEM images were taken to investigate the surface morphology of the activated carbon using an SEM: Carl Zeiss (SUPRA 55, Germany) by field emission scanning electron microscopy. Furthermore, the surface carbon–oxygen functional groups present in samples were identified by performing FTIR measurements using the KBr method by FTIR – Fourier transform infrared spectroscopy (ALPHA FTIR Spectrometer, Bruker). FTIR studies were carried out between 4,000 and 500 cm−1 for all the samples.

Preparation of biodiesel wash water from waste cooking oil

Here, 50 L waste cooking oil (WCO) was collected from the mess hall facility at Sathyabama Institute of Science and Technology, Tamil Nadu, India. The free fatty acid (FFA) content of the collected WCO was tested as per ASTM D664. The FFA content was determined using a sodium hydroxide (NaOH) titration method. The WCO was transesterified using methanol 1:3 molar ratio and NaOH as a catalyst for a time of 90 min in a 100 L capacity biodiesel pilot plant established at the Centre for Waste Management, Sathyabama Institute of Science and Technology, Chennai, Tamil Nadu, India. Biodiesel was separated from the byproduct (crude glycerol) after a settling time of 8 h at room temperature. Later the biodiesel was collected and subjected to wet washing (Ranjan et al. 2018):
formula
(1)

The collected biodiesel was washed with hot water at 60–80 °C for 15 min. Due to density difference, the washed biodiesel remained at the top allowing the wash water to settle at the bottom. The collected wash water was tested for its pH and the washing cycle was repeated until the pH of wash water collected became neutral (Nirmala et al. 2020). Depending on the quality of the WCO used as the raw material, the number of washing cycles varied from 3 to 5. Wash water generated during each cycle of washing was collected and used for adsorption studies.

Adsorption studies

Here, 0.5 g of ZnCl2 activated carbon was added to 100 mL of biodiesel wash water and agitated in a stoppered conical flask at constant speed of 120 rpm for 2 h. The mixture was filtered using a Whatman filter paper (110 mm). Wash waters after treatment with food waste activated carbon from all four samples (WCVR, MFPW, WCR and MFW) were analyzed as per standards (Wong et al. 2018) and their properties (pH, turbidity, COD, oil and grease) were determined.

RESULTS AND DISCUSSION

Proximate analysis

The proximate analysis of the food waste samples are represented in Table 1. It was observed that the fixed carbon percentages of all samples fell between 22 and 32 comparable with the previously reported literature (Bashir et al. 2018) and were found to be suitable for activated carbon synthesis. It was observed that food waste with no rice content, comprising of only fruit peels (B) has a higher percentage fixed carbon, while for other samples fixed carbon was found to increase with increasing cooked rice percentage. The moisture content, ash content and volatile matter of the samples WCVR, MFPW, WCR, MFW were also comparable to the proximate composition (Sayğılı et al. 2015). The samples WCVR, MFPW, WCR and MFW had 65.91%, 53.44%, 60.92% and 54.21% moisture content, 0.026%, 5.01%, 1.56% and 13.42% ash content, and 10.9%, 10.20%, 10.35% and 9.74% volatile content, respectively.

Table 1

Comparison of proximate analysis of collected food waste with previously published literature

SampleMoisture content (%)Ash content (%)Volatile mater (%)Fixed carbon (%)References
WCVR 65.91 0.026 10.19 23.86 In this study 
MFPW 53.44 5.01 10.20 31.346 
WCR 60.92 1.56 10.35 27.17 
MFW 54.21 13.42 9.74 22.62 
Food waste 60.9 1.61 80.9 11.4 Chen et al. (2019a)  
Food waste 74 1.15  24.85 Chen et al. (2019b)  
Food waste 76.5 6.4 79.1 14.5 Saqib et al. (2018)  
Kitchen waste 60–85 3.5–5.5 – 18–30 Chang et al. (2006)  
SampleMoisture content (%)Ash content (%)Volatile mater (%)Fixed carbon (%)References
WCVR 65.91 0.026 10.19 23.86 In this study 
MFPW 53.44 5.01 10.20 31.346 
WCR 60.92 1.56 10.35 27.17 
MFW 54.21 13.42 9.74 22.62 
Food waste 60.9 1.61 80.9 11.4 Chen et al. (2019a)  
Food waste 74 1.15  24.85 Chen et al. (2019b)  
Food waste 76.5 6.4 79.1 14.5 Saqib et al. (2018)  
Kitchen waste 60–85 3.5–5.5 – 18–30 Chang et al. (2006)  

WCVR, Kitchen waste (rice, vegetables, oil and spice); MFPW, Mixed fruit peels; WCR, Mess hall waste (plain rice); MFW, Mixed food waste (rice, dhal, vegetables, fruits, meat and bones).

Structural and surface characterization

X-ray diffraction (XRD) measurements

The X-ray diffraction technique was used to interpret the influence of ZnCl2 treatment on activating food waste carbon. Carbon powder was prepared for XRD analysis by grinding the required amount at 80 °C for 2 h. The typical broad diffraction peak was obtained at 22.3° and 42° corresponding to (002) and (101) planes respectively. This indicated the presence of dominant amorphous phase (Figure 1). It is also noted that the XRD pattern of waste cooked rice (WCR) (Chingombe et al. 2005) showed a high intensity peak (002) with increased broadening without any secondary peaks which indicated that the carbon atoms existed in highly distorted manner compared with the other samples (Rajbhandari et al. 2012; Danish et al. 2018).

The diffraction pattern (Figure 2) of the ZnCl2 treated activated carbon samples confirmed the formation of ZnO which has absorbed on to the carbon surface after ZnCl2 treatment. The appearance of high intensity peaks at 31.9°, 34.5° and 36.5° indicate the crystalline hexagonal phase of ZnO (JCPDS# 36-1451) as all the samples were dried at 600 °C in an air atmosphere. The addition of ZnCl2 significantly affected the amorphous nature of the carbon phase as it can be seen that the intensity had changed for all the samples (Zięzio et al. 2020). Interestingly, the amorphous carbon peak had completely disappeared for cooked vegetable rice (WCVR) and the mixed fruit peel waste (MFPW) sample, whereas the amorphous peak still appeared for the WCR and mixed food waste sample (MFW). The results strongly revealed that the ZnCl2 activation had stabilized the amorphous carbon phase in the WCR and mixed food waste sample (MFW). It was evident that the crystalline nature of carbon had improved in the ZnCl2 activated WCR sample compared with the untreated sample as reduced peak broadening is observed.

Field emission scanning electron microscopy (FESEM)

The surface morphology for adsorbents obtained from different food waste materials varied significantly. Specifically ZnCl2 activated adsorbent synthesized from rice was observed to have a mesoporous surface (Rajbhandari et al. 2012; Mokhtar et al. 2013) which is very important from the water treatment point of view and can handle wide ranges of pollutants including heavy metals, surfactants and high molecular weight organic pollutant (Mokhtar et al. 2013). ZnCl2 activation enhanced the stability and mesoporosity of the carbonaceous material and depicted the changes in surface morphology of carbonaceous samples after ZnCl2 activation (Figures 3 and 4). The activation process brought changes in the surface of the adsorbents. From the results, it is evident that ZnCl2 activation has been effective on waste rice as uniform pore (mesoporous) distribution was observed (Bae et al. 2014). Also, the FESEM data have been analyzed further and it was observed that the food waste-based activated carbon was 44.87 nm in size and the activated carbon synthesized from other food waste materials also had particles of size less than 100 nm, leading to the conclusion that the food waste carbonaceous materials yield nanoparticles upon ZnCl2 activation.

FTIR spectroscopy

Some important functional groups were identified in the synthesized activated carbon samples by FTIR spectroscopy as shown in Figure 5. It is evident that the peaks at 1,006.02 cm−1, 1,026.56 cm−1 are responsible for C-O stretching and 2,346.71 cm−1, 2,352.87 cm−1, 2,359.03 cm−1 and 3,783.90 cm−1, 3,788.01 cm−1 for O-H stretching in esters (Yagmur et al. 2008). The peaks 1,061.46 cm−1, 1,320.15 cm−1, 1,248.29 cm−1, 1,139.48 cm−1 and 1,162.06 cm−1 correspond to the C-N stretching in aliphatic amines and the peaks at 3,395 cm−1and 3,338 cm−1 indicate the broad vibrational band caused by N-H stretching. The peak at 1,724.62 cm−1 corresponds to the C = O stretching in ketones. The peaks at 2,915.43 cm−1, 2,921.75 cm−1 and 2,931.85 cm−1 indicate the C-H stretching in alkanes. The 1,603.48 cm−1, 1,609.64 cm−1, 1,605.54 cm−1 peaks indicate the C = C stretching in alkenes and the peak at 1,449.50 cm−1 indicates the C = C stretching in aromatic compounds (Saka 2012; Jaria et al. 2019) (Figure 6). Indication of the decomposition of alkane and ester functional groups as the peaks in the spectral range around ∼2,300 cm−1–3,000 cm−1 is not evident for all the samples (WCVR, MFPW, WCR, MFW). Most of the frequencies attributed to the activated carbon were absent and were mainly due to the existence of volatile organic compounds at an activation temperature in the range of 500–600 °C. However, the observation of transmission peaks of ZnCl2 treated samples in the range ∼ 1,000 cm−1–3,500 cm−1 may be attributed to the activated carbon samples attached to the surface groups bearing oxygen atoms on the aromatic and aliphatic backbone skeletons. The significant shifts of peaks between the samples may be predicted to be due to the interactions that originate from different activated functional groups (Ahmaruzzaman & Gupta 2011).

Biodiesel and wash water characterization

The moisture content, density, FFA, kinematic viscosity, resistance to corrosion, cloud and pour point, flash and fire point and calorific value of WCO were determined. Free fatty acid of WCO was found to be 0.11%, which helped in the choice of biodiesel production by the single stage transesterification process. Here, 1 mol of WCO was transesterified with 3 moles of methanol in the presence of alkali catalyst (5 g/L) at 60 °C for 90 min. Biodiesel yield was 97.3%, wash water formation after wet washing was 133 L and crude glycerol (byproduct) yield was 6.9 L. Density, kinematic viscosity and flash point of WCO before and after transesterification are given in Table 2. The properties were determined following ASTM International standards and it is evident that transesterification has yielded a fuel compatible to that used in diesel engines either in pure form or in blends. The collected wash water was characterized: a pH of 10, turbidity of 63 NTU, COD of 150 mg/L and oil and grease of 98 mg/L were determined.

Table 2

Physiochemical properties of waste cooking oil and biodiesel

ParametersASTM standardsWCO propertiesWCOBD properties
Density (g/cc) ASTM D792 0.925 0.875 
Kinematic viscosity @ 40 °C (cSt) ASTM D445 9.38 2.18 
Flash point by PMCC method (°C) ASTM D93 245 189 
Fire point by PMCC method (°C) ASTM D93 261 202 
Copper strip corrosion @60 °C ASTM D130 1a (slight tarnish) 1a (slight tarnish) 
Cloud point (°C) ASTM D2500 12 
Pour point (°C) ASTM D2500 
Moisture content (%) ASTM D2709 2.6 0.021 
Acid value ASTM D664 0.11% 0.218 mg NaOH/g of biodiesel 
Calorific value (cal/g) ASTM D480913 9,598.5 8,522.978 
ParametersASTM standardsWCO propertiesWCOBD properties
Density (g/cc) ASTM D792 0.925 0.875 
Kinematic viscosity @ 40 °C (cSt) ASTM D445 9.38 2.18 
Flash point by PMCC method (°C) ASTM D93 245 189 
Fire point by PMCC method (°C) ASTM D93 261 202 
Copper strip corrosion @60 °C ASTM D130 1a (slight tarnish) 1a (slight tarnish) 
Cloud point (°C) ASTM D2500 12 
Pour point (°C) ASTM D2500 
Moisture content (%) ASTM D2709 2.6 0.021 
Acid value ASTM D664 0.11% 0.218 mg NaOH/g of biodiesel 
Calorific value (cal/g) ASTM D480913 9,598.5 8,522.978 

Adsorption using food waste activate carbon samples

The pH, turbidity, COD, oil and grease of biodiesel wash water before and after treatment are listed in Table 3. It is evident that water quality parameters tested were reduced considerably by treatment with ZnCl2 food waste activated carbon (Bashir et al. 2018), paving the way to carry out detailed investigations and optimization of adsorption conditions.

Table 3

Pollutant removal efficiency of food waste-based activated carbon from biodiesel washwater

Source of activated carbonpH
Turbidity (NTU)
% RemovalCOD (mg/L)
% RemovalOil and Grease (mg/L)
% Removal
InitialFinalInitialFinalInitialFinalInitialFinal
WCVR 10 ± 0.1 7.2 ± 0.2 63 ± 0.008 1 ± 0.1 98.41 150 ± 0.18 91 ± 0.9 39.33 98 ± 0.2 0.938 ± 0.01 99.04 
MFPW 10 ± 0.2 6.9 ± 0.3 63 ± 0.1 1 ± 0.23 98.41 150 ± 3 84 ± 0.3 44 98 ± 0.15 0.92 ± 0.08 99.06 
WCR 10 ± 0.1 6.8 ± 0.15 63 ± 0.12 1 ± 0.2 98.41 150 ± 0.5 89 ± 0.23 40.66 98 ± 0.21 0.926 ± 0.02 99.05 
MFW 10 ± 0.2 6.5 ± 0.21 63 ± 0.8 1 ± 0.3 98.41 150 ± 0.82 88 ± 0.36 41.33 98 ± 0.08 0.925 ± 0.01 99.05 
Source of activated carbonpH
Turbidity (NTU)
% RemovalCOD (mg/L)
% RemovalOil and Grease (mg/L)
% Removal
InitialFinalInitialFinalInitialFinalInitialFinal
WCVR 10 ± 0.1 7.2 ± 0.2 63 ± 0.008 1 ± 0.1 98.41 150 ± 0.18 91 ± 0.9 39.33 98 ± 0.2 0.938 ± 0.01 99.04 
MFPW 10 ± 0.2 6.9 ± 0.3 63 ± 0.1 1 ± 0.23 98.41 150 ± 3 84 ± 0.3 44 98 ± 0.15 0.92 ± 0.08 99.06 
WCR 10 ± 0.1 6.8 ± 0.15 63 ± 0.12 1 ± 0.2 98.41 150 ± 0.5 89 ± 0.23 40.66 98 ± 0.21 0.926 ± 0.02 99.05 
MFW 10 ± 0.2 6.5 ± 0.21 63 ± 0.8 1 ± 0.3 98.41 150 ± 0.82 88 ± 0.36 41.33 98 ± 0.08 0.925 ± 0.01 99.05 

WCVR, Kitchen waste (rice, vegetables, oil and spice); MFPW, Mixed fruit peels; WCR, Mess hall waste (plain rice); MFW, Mixed food waste (rice, dhal, vegetables, fruits, meat and bones).

pH is the measure of alkalinity or acidic nature of a solution. WHO in 1958 instructed that pH for domestic usage of water (drinking, washing, etc.) has to be 6.5–9.2. Later, the pH of commercial usage of water was changed to 6.5–8.5. In this study the effect of activated carbon on pH reduction of biodiesel wash water was explored with 100 mL of wash water, 0.5 g of activated carbon at time of 60 min and agitation at 150 rpm. From the results (Table 3), the pH of the wash water was reduced to 6.5 from 10 for the activated carbon produced from MFW. The pH of wash water was reduced to 7.2, 6.9 and 6.8 respectively when treated with activated carbon produced from other wastes (WCVR, MFPW, WCR) used in the study. Recently, ZnCl2 incorporated activated carbon (3.2 g) produced from wastepaper and cotton reduced the pH to 8.21 from 9.43 with reduction efficiency of 12.9% (Mustafa & Asmatulu 2020).

Turbidity of the solution depends upon the presence of a large number of suspended solids, which results in cloudiness of the solution. Turbidity is also one of the parameters that define the quality of water. Quality of water is inversely proportional to the value of turbidity. The turbidity of drinking water should not exceed 5 NTU (Girotto et al. 2015). In this study the effect of food waste activated carbon on turbidity reduction of biodiesel wash water was also explored. From the results (Table 3), it is evident that the turbidity of the wash water reduced to 1 NTU from 63 NTU for the activated carbon produced from mixed food waste (MFW). The turbidity reduction efficiency was 98.41%. The turbidity of the wash water obtained after treatment with activated carbon produced from other wastes (WCVR, MFPW, WCR) was also reduced to 1 NTU respectively. Recently, ZnCl2 incorporated activated carbon (3.2 g) produced treated water of 1.8 NTU from an effluent of 147 NTU with reduction efficiency of 98.77% after removal of 147 NTU turbidity showing 98.77% efficiency (Girotto et al. 2015).

It is evident from Table 3, that the COD of the wash water was reduced to 88 mg/L with activated carbon produced from MFW. The COD reduction efficiency was 41.33% .The COD of the wash water treated with activated carbon produced from other wastes (WCVR, MFPW, WCR) were 91, 84 and 89 mg/L, respectively. The oil and grease was reduced to 0.952 mg/L from 98 mg/L under the optimum adsorption conditions when MFW activated carbon was used. The removal efficiency of activated carbon with respect to oil and grease was found comparable at 99.5% (Santos et al. 2020). The activated carbon produced from other waste (WCVR, MFPW, WCR) also proved effective in oil and grease reduction to 0.938, 0.925 and 0.926, respectively.

CONCLUSION

As outcomes of this study, the fixed carbon percentages of MFW samples were found to be between 22 and 23% which shows the applicability of MFW samples for the synthesis of ZnCl2 activated carbon nanomaterial as evident from the FESEM data indicating nanoparticles of 44.87 nm. The uniform pore mesoporous distribution surface of ZnCl2 activated adsorbent was been observed under FESEM analysis, and is an important factor required for the use of activated carbon in water treatment. The ZnCl2 activated food waste carbon proved effective in treating biodiesel wash water as it reduced the pH to neutral, turbidity to 1 NTU, COD to 88 mg/L and oil and grease to 0.925, making the treated water suitable for reuse.

ACKNOWLEDGEMENTS

The authors thank the Ministry of Human Resource Development, Government of India for funding the research work (Award No. 5-5/2014-TS.VII 4 September 2014). The authors thank the Physics Department, Sathyabama Institute of Science and Technology for FT IR analysis and the Centre for Nanoscience and Nanotechnology Sathyabama Institute of Science and Technology for FESEM.

CONFLICT OF INTEREST

None.

DATA AVAILABILITY STATEMENT

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

REFERENCES

Abdul-Hameed
H. M.
Al Juboury
M. F.
2020a
MgFe-doubled layers hydroxide intercalated with low cost local adsorbent using for removal of lead from aqueous solution
.
J. Water Land Dev.
45
(
IV–VI
),
10
18
.
doi:10.24425/jwld.2020.133041
.
Abdul-Hameed
H. M.
Al Juboury
M. F.
2020b
A novel coated of Mg/Fe layered double hydroxide on date palm stones.
IOP Conf. Ser.: Earth Environ. Sci.
464
,
012003
.
Ahmaruzzaman
M.
Gupta
V. K.
2011
Rice husk and its ash as low-cost adsorbents in water and wastewater treatment
.
Ind. Eng. Chem. Res.
50
,
13589
13613
.
Baldev
E.
Mubarakali
D.
Saravanakumar
K.
Arutselvan
C.
Alharbi
N. S.
Alharbi
S. A.
Sivasubramanian
V.
Thajuddin
N.
2018
Unveiling algal cultivation using raceway ponds for biodiesel production and its quality assessment
.
Renew. Energy
123
,
486
498
.
Bashir
M. J. K.
Aziz
H. A.
Amr
S. S. A.
Sethupathi
S. A. P.
Ng
C. A.
Lim
J. W.
2015
The competency of various applied strategies in treating tropical municipal landfill leachate
.
Desalin. Water Treat.
54
,
2382
2395
.
Chang
J. I.
Tsai
J. J.
Wu
K. H.
2006
Thermophilic composting of food waste
.
Bioresour. Technol.
97
,
116
122
.
Chen
J.
Fan
Y.
Jiaqiang
E.
Cao
W.
Zhang
F.
Gong
J.
Liu
G.
Xu
W.
2019a
Effects analysis on the gasification kinetic characteristics of food waste in supercritical water
.
Fuel
241
,
94
104
.
Chen
W.-H.
Lin
Y.-Y.
Liu
H.-C.
Chen
T.-C.
Hung
H.-C.
Chen
C.-H.
2019b
Analysis of physicochemical properties of liquefaction bio-oil from food waste
.
Energy Procedia
158
,
61
66
.
Chingombe
P.
Saha
B.
Wakeman
R. J.
2005
Surface modification and characterisation of a coal-based activated carbon
.
Carbon N. Y.
43
,
3132
3143
.
Chung
Z. L.
Tan
Y. H.
San Chan
Y.
Kansedo
J.
Mubarak
N. M.
Ghasemi
M.
Abdullah
M. O.
2019
Life cycle assessment of waste cooking oil for biodiesel production using waste chicken eggshell derived CaO as catalyst via transesterification
.
Biocatal. Agric. Biotechnol.
21
,
101317
.
Dabwan
A. H. A.
Yuki
N.
Asri
N. A. M.
Katsumata
H.
Suzuki
T.
Kaneco
S.
2015
Removal of methylene blue, rhodamine B and ammonium ion from aqueous solution by adsorption onto sintering porous materials prepared from coconut husk waste
.
Open J. Inorg. Non-Met. Mater.
5
,
21
.
Danish
M.
Ahmad
T.
Hashim
R.
Said
N.
Akhtar
M. N.
Mohamad-Saleh
J.
Sulaiman
O.
2018
Comparison of surface properties of wood biomass activated carbons and their application against rhodamine B and methylene blue dye
.
Surf. Interfaces
11
,
1
13
.
Dhandapani
E.
Duraisamy
N.
Raj
R. M.
2020
Green synthesis of carbon quantum dots from food waste
.
Mater. Today Proc.
in press https://doi.org/10.1016/j.matpr.2020.10.025
Dizbay-Onat
M.
Vaidya
U. K.
Balanay
J. A. G.
Lungu
C. T.
2018
Preparation and characterization of flax, hemp and sisal fiber-derived mesoporous activated carbon adsorbents
.
Adsorpt. Sci. Technol.
36
,
441
457
.
Enaime
G.
Ennaciri
K.
Ounas
A.
Baçaoui
A.
Seffen
M.
Selmi
T.
Yaacoubi
A.
2017
Preparation and characterization of activated carbons from olive wastes by physical and chemical activation: application to Indigo carmine adsorption
.
J. Mater. Environ. Sci.
8
,
4125
4137
.
Girotto
F.
Alibardi
L.
Cossu
R.
2015
Food waste generation and industrial uses: a review
.
Waste Manag.
45
,
32
41
.
Guan
B. T. H.
Latif
P. A.
Yap
T. Y. H.
2013
Physical preparation of activated carbon from sugarcane bagasse and corn husk and its physical and chemical characteristics
.
Int. J. Eng. Res. Sci. Technol.
2
,
1
14
.
Halim
A. A.
Aziz
H. A.
Johari
M. A. M.
Ariffin
K. S.
Bashir
M. J. K.
2012
Semi-aerobic landfill leachate treatment using carbon–minerals composite adsorbent
.
Environ. Eng. Sci.
29
,
306
312
.
Joshi
V. K.
2002
Food processing industries’ waste: opportunities, technologies, challenges and future strategies
. In:
Biotechnology in Agriculture and Environment
(J. K. Arora, S. S. Marwaha & R. Grover, eds). New Delhi: Asiatech Publishers Inc., pp.
129
148
.
Kosheleva
R. I.
Mitropoulos
A. C.
Kyzas
G. Z.
2019
Synthesis of activated carbon from food waste
.
Environ. Chem. Lett.
17
,
429
438
.
Mahamad
M. N.
Zaini
M. A. A.
Zakaria
Z. A.
2015
Preparation and characterization of activated carbon from pineapple waste biomass for dye removal
.
Int. Biodeter. Biodegr.
102
,
274
280
.
Mokhtar
M. F.
Latib
E. H. A.
Sufian
S.
Shaari
K. Z. K.
2013
Preparation of activated carbon from durian shell and seed
.
Adv. Mater. Res
.
626
,
887
891
.
Pandey
B. K.
Vyas
S.
Pandey
M.
Gaur
A.
2016
Municipal solid waste to energy conversion methodology as physical, thermal, and biological methods
.
Curr. Sci. Perspect
2
,
39
44
.
Pitakpoolsil
W.
Hunsom
M.
2013
Adsorption of pollutants from biodiesel wastewater using chitosan flakes
.
J. Taiwan Inst. Chem. Eng.
44
(
6
),
963
971
.
Poornapushpakala
S.
Dawn
S. S.
Govind
M. A.
Santhosh
A.
Nirmala
N.
Barani
S.
Nirmala
M.
2021
A novel image processing technique to evaluate biodiesel wastewater for recovery, recycle and reuse towards zero liquid discharge approach
.
Biocatal. Agric. Biotechnol.
31
,
101874
.
Ramakrishnan
K.
Namasivayam
C.
2009
Development and characteristics of activated carbons from Jatropha husk, an agro industrial solid waste, by chemical activation methods
.
J. Environ. Eng. Manag.
19
,
173
178
.
Santos
T. M.
de Jesus
F. A.
da Silva
G. F.
Pontes
L. A. M.
2020
Synthesis of activated carbon from Oleifera moringa for removal of oils and greases from the produced water
.
Environ. Nanotechnol. Monit. Manag.
14
,
100357
.
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