Sugarcane industries have a major contribution to the rural development of country, including pollution level to the environment. Associate with all the waste from the sugarcane industry, wastewater is a key issue to manage. Throughout the sugarcane processing season, large quantities of water consumed and discharge a large amount of wastewater. The investigation has been done to bring wastewater up to recycling limit made by pollution board. The objective of this research work is to reduced the pollutants from sugar industry effluent with thermal oxidation, electrooxidation, and combined with both treatment process. The result shows 68.5% COD and 71.2% color with thermal, 82.5% COD, and 86.5% color with electrocoagulation and 98% COD and 99.2% color reduction with a combined treatment of most appropriate conditions. In settling and filtration study 80% of efficiency was attained with the combined study. The sludge containing a lesser amount of inorganic and treated can be reutilized.
Sugarcane is an essential crop for human life. It was introduced to Egypt around 647 A.D. and, about one century later, to Spain (755 A.D.) . Sugar produced from sugarcane and globally sugar production was estimated 179.3 million in the year of 2018–2019 by FAO . Sugar production is the seasonal business (Dec–June), but lots of water was required for processing, and half of the ratio discharged as effluent. The wastewater from sugar industry has a high degree of oxygen demand suspended and other non-toxic contaminants . The degree of pollutants varies according to production crushing capacity of sugar industries. The effluent comes out from sugar industry have major effects on surrounding air, groundwater, rural agricultural land, and human health's . Generally conventional (physical, chemical and biological) treatment process were applied to reduced the pollutant level from sugar processing plant effluent, which is unable to bring treated water up to the recycling level . The characteristics of wastewater also depend on the nature of industries. Due to that common practice wastewater treatment plants unable to treat the wastewater .
Different techniques were introduced to treat the wastewater, but it was failure might be due to performance or economical point of view . Some methods like thermal oxidation, electrochemical oxidation have been modified with their design, material used, and operating conditions and implement in different industry wastewater. Thermolysis is one of the recent and novel technologies, which employed in the pulp and paper ; distillery ; petrochemical  and sugar industry  wastewater etc. Thermal treatment is the process of chemical modification of the total organic and inorganic with or without chemical salts at a modest atmospheric condition (temperature and pressure). The interactions among chemical salts and dissolved present in wastewater need the temperature to split chemical bonds . The organic and inorganic in wastewater either get polymerized/ or decomposed into smaller molecules and precipitated like coagulation process . The electrocoagulation process is the development version of chemical coagulation process. The electrocoagulation suggests as a substitute for using metal salt or polymer and polyelectrolyte addition to split the stable emulsion and suspension in wastewater by employing electricity . The technology capable of eliminates metal, colloidal particles and soluble inorganic pollutants from the effluent by using high charge polymeric metal hydroxide spices . These spices neutralize the electrostatic charge on suspended solid to facilitate agglomeration and resultant separation from the aqueous medium . Electrochemical shows high efficiency in the treatment of textile wastewater , Bilge wastewater , Agro-industry wastewater , etc. Traditional methods have so many drawbacks like more space requirements, a large number of equipment and accessories, a large amount of chemicals for removal of suspended including sludge production, complicated to manage, or operate . As compared to this burden, thermolysis and electrochemical treatment processes have been demonstrated to be very efficient in reducing the pollutants from effluent and are characterized by removal of waste production, low demand of chemicals, and straightforward process. Therefore water management in the sugar industry needs specific attention .
The goal of this investigate is to reduced the pollutants from sugarcane processing industry effluent up to a dischargeable limit. The treatment of sugar industry wastewater was carried out by thermolysis, electrocoagulation, and combined with thermal oxidation and electrooxidation processes. The study optimized the most suitable operating conditions like initial pH, mass loading and working temperature to treat the sugar industry effluent. The treated effluent was also characterized by settling, filtration, and thermal analysis.
Material and Methods
The effluent was collected from Bhoramdeo Sugar Factory (BSF) Kawardha Chhattisgarh and characteristics are tabulated in Table 1. Standard laboratory-grade chemical was purchased from Merk Chemicals, Bombay, and used without any purification.
Thermolysis of wastewater was carried in a three-necked glass reactor. The capacity of the reactor is 500 ml, the necked fitted with a temperature sensor to measure the temperature variation, condenser to condensed heated sample, and high heat resistance crock for sample collection. A magnetic stirrer was employed to maintain the uniformity of wastewater with the catalyst. The complete system has been fixed in the digital thermal plate. The calculated amount of wastewater and catalyst was heated in the range of 55 to 95 °C temperature. A small amount of treated wastewater was withdrawn in fixed time and analysis for chemical oxygen demand and color reduction. The characteristic of catalyst used in the experiment is mention in Table 2.
An electrochemical reactor made up of transparent fiberglass having heat resistance up to 100 °C. A magnetic stirrer was employed with the digital plate. Four electrodes in terms of two pairs (anodes and cathodes) were inserted into the electrochemical reactor and connected with DC power supplies in parallel mode . An electrochemical process for pollutant removal operation is presented in Fig. 1. The current applied and voltage variation was measured with help of ammeter and voltmeter. The treated wastewater was collected at a fixed interval of time for COD and color removals. The dimension of the reactor is given in Table 3.
The required pH (pH 2–pH 10) of the sample was adjusted by using either 0.1 N hydrochloric acid (HCl) or 1 M sodium hydroxide (NaOH). The color of the sugar industry wastewater samples before and after the thermal treatment (TT) and electrocoagulation (EC) was measured by a UV–vis spectrophotometer. A small amount of treated samples were taken out from AGR and ECR and its reduction was determined. The fraction of chemical oxygen demand and color reduction in terms of percentage was determined according to Eq. (1), .
where Ci is the initial concentration and Cf is the final concentration at t (min) after thermolysis and electrolysis.
All the physical and chemical pollutants such as chemical oxygen demand, color, total suspended and dissolved solids, reduced carbohydrate, sulfate, chloride, etc., was examine as per standard method of analysis . The color of the sample was measured in terms of the absorbance at λ = 420 nm using a UV–vis spectrophotometer (Model Lambda 35) from Perkin-Elmer Instruments, Switzerland. Settling has been done with 500 ml measuring cylinder and filtration study by using filter paper (What’s man 42 No) and Buechner funnel. The Thermal investigation (TGA/DTGA/DTA) of the untreated and treated with iron electrode sludge was examined by using a TG analyzer (Pyris Diamond, Perkin-Elmer) with 10 °C/min of constant heating rate and under nitrogen flow as an inert gas. The XRD analysis was performed on BRUKE-D8 diffracto meter. A source of Cu-Kα radiation was used and scan was taken from 2θ = 10 to 2θ = 90 at room temperature of 25 °C.
Experimental Values and Discussion
Processing with Chemical Salt
Role of Adjusted pH on Pollutant Removal
The initial COD (3682 mg/l) and color (350PCU) removal efficiency of sugar industry wastewater was investigated with ferrous sulfate (FeSO4), copper sulfate (CuSO4), aluminum sulfate (Al2(SO4)3) and without chemical salt. The pH range varies between pH 2 to pH 10 at fixed working temperature 75 °C, mass loading 4Kg/m3, and treatment time 4hrs. The results expressed as a graphical form shown in Fig. 2a, b. It was observed that a maximum 52.4% COD and 55% color removal shown by aluminum sulfate at pH 8, then ferrous sulfate 47.4% COD and 50.2% color at pH 10 and copper sulfate 46.4% cod and 48.5% color at pH 8. When wastewater treated without chemical salt the removal efficiency was 17% COD and 19.2% color at pH 6. This might be due to nature of wastewater, which forms active positive charge at different pH range . Positive charges have enough capability to defuse the negative charges, the formation of flock, and settle down .
Role of Catalyst Dosing and eExperimental Temperature
The significance of mass loading was carried out at the range of 2–10 Kg/m3 with aluminum sulfate at optimum pH 8, temperature 75 °C for 4 h which shown in Fig. 3a. It was noticed that with increase in mass loading 2 kg/m3, 4 kg/m3, 6 kg/m3, 8Kg/m3 the removal efficiency of COD 41%, 52.4%, 58.9%, 63.5% and color 43.8%, 55%, 61.4% 68% removal was increased. Further increase in mass loading 10Kg/m3 decrease performance 60% COD and 63.1% color removal respectively. The main reason behind the increasing and decreasing of performing with mass loading is the formation of positive ion formation. At low dosing, it is not sufficient to naturalize the negative ion and at high dosing, destabilization occurred again. That why optimum mass loading has a major role for maximum removal of pollutants . The experiments were also performed at different temperatures ranges at fixed alkalinity of samples and salt dosing, which presented in Fig. 3b. At low temperature range 55 °C, 65 °C and 75 °C the COD 51.2%, 57% 63.5% and color 55%, 59.4%, 68% was observed. This might be due to low energy, which is insufficient to break the functional bond present in sugar industry wastewater. At 85 °C experimental temperature COD, 68.5% and color 71.2% reduction was found, which height efficiency with thermolysis treatment. Additionally when the temperature increases to 95 °C the performance decrease to 65.4% COD and 69.1% color removal respectively. This attributes to the re-dissolutions of pollutants again in treated wastewater at more temperature .
Treatment with Electro-oxidation
Role of Initial pH
To treat the sugar industry wastewater with electrocoagulation, the parameters were optimized with an iron electrode, an aluminum electrode and a copper electrode at initial COD 3682 mg/L, color 350PCU, treatment time 120 min (2 h), space between electrode 2 cm, current density 78 Am−2. The pH range varies between 2 to 10 pH, which shown in Fig. 4. The result indicates that aluminum electrode shows a maximum 70% COD and 73.5% color reduction at pH 7. Further, an increase in pH decrease the performance with respect to time. An iron electrode shows 61% COD and 65% color removal and copper electrode show 68% COD and 72.1% color removal at pH 6. This attributes to the formation of hydroxide and poly hydroxide metal ions at acidic and alkaline nature of wastewater water . Sugar industry wastewater containing different functional and amino groups, which react at a particular pH of wastewater .
Role of Current Density in Terms of Mass Loading
Current density is directly proportional to ions added to the aqueous solution, which affects the electrochemical treatment efficiency. To investigate the effect of current density (39–195 Am−2) on ions consumption was carried out at fixed pH 7, electrode distance 20 mm for 120 min. The result represented in Fig. 5a. From Fig. 5a, it can be see that with increase in current density 39 Am−2, 78 Am−2, 117 Am−2, 156 Am−2, the COD removal 68%, 71%, 76.8%, 82.5% and color removal 72.1%, 74.5%, 79.5%, 86.5% increase, beyond that COD 78.2% and color 81.4% decrease for 195 Am−2. Electrocoagulation acts similar to thermolysis means at low dosing ions are not enough to neutralize the negative ion and high dosing increase the number of ions that decrease the removal performance (zeta potential increases). The consumption of ion with respect temperature is presented in Fig. 5b. It has been noticed that ions consumption and temperature increase with an increase in current density, at maximum COD (82.5%), and color (86.5%) reduction, it was 0.84 g. Similarly, the temperature was also found to increase 72 °C, 76 °C, 83 °C, 86.4 °C, 89 °C with an increase in current from 39 to 195Am−2. This attributes to anodic dissolution increase with current density, which increases the amount of aluminum precipitate and temperature .
Thermal-oxidation along with electrooxidation The percentage removal of chemical oxygen demand (3682 mg/l) and color (350PCU) with electrocoagulation (COD 644 mg/l, color 47.25 PCU) and thermolysis (COD 1160, color 100PCU) was compared at most favorable condition is shown in Fig. 6a. It has perceived that thermolysis treatment is not able to treat the sugar industry wastewater up to acceptable norms. The leftover achieved after chemical salt-treated was process with electrochemical at optimal conditions shows more effective in treating the effluent than the singly treatment processes, which shown in Fig. 6b. The results reveal that an experimental time 20 min is adequate to bring COD 98% (73 mg/l) and color removal 99.2% (2.8CPU) from initial COD and color of sugar industry wastewater. The reason might be due to effects of thermolysis is not sufficient to reduce the pollutant from SIWW and combined treatment was more effective than single treatment .
Investigation of Separated Solid and Liquid
Sedimentation process has significant role in the wastewater treatment process; it shows the efficiency of treatment. To examine the separation potential of thermal treatment, electrochemical treatment, and combined treatment, an experiment conducted in 500 ml of measuring cylinder with the help of a stopwatch. The solid–liquid separation with respect to time is shown in Fig. 7a. It was observed that aluminum electrode (electrochemical) treated wastewater shown good separation in 120 min, almost 10:90 solid–liquid was found. Nearly 80% (20:80 solid–liquid) separation was noticed for combined treated wastewater and 60% (40:60 solid liquid) with thermally treated wastewater. This might be due to heavy flock formation after electrochemical treatment . The physical characteristics of sludge were analyzed and mentioned in Table 4.
The gravity filtration was carried out in laboratory grade filter paper with help of Buchner funnel, under atmosphere condition. The filtrate volume collected with respect to time versus total volume was plotted for thermal, electrochemical, and combined treated wastewater at optimum condition, that presented in Fig. 7b. The resistance of filter medium and filter cake was calculated by using Eq. (2) [32, 33]:
where time difference denoted with (Δt), volume collected in certain time denoted with (ΔV), concentration of solid in slurry denoted with ( C), volume of filtrated liquid in time differences is denoted with (V), kinematic viscosity of filtered liquid is denoted with (µ), specific resistance (α) pressure difference in liquid is denoted with (ΔP = ρgh), area (A) and resistance (Rm) of filter medium were used. After determining the value of filtrate with respect to time, a diagonal line between Δt/ΔV and V was obtained. The values of filter medium resistance (Rm) and specific resistance (α) were cslculated from the diagonal line and presented in Table 5. The values of α 0.284 × 10–14, 0.451 × 10–14, 0.546 × 10–14 m/Kg and Rm 0.131 × 10–12, 2.15 × 10–12, 4.34 × 10–12 were achieved for electro-oxidation process, joint process and thermal-oxidation process.. From the result, it can found that electrochemically treated wastewater has more prose and spongy as compared to others .
The complete decomposition of untreated and treated with iron electrodes sludge of sugar industry wastewater was examine with thermal gravimetric analysis at atmospheric conditions. The peaks of thermal gravimetric analysis (TGA), differential thermal analysis (DTA) and differential thermal gravimetry (DTG) are presented in Fig. 8a, b respectively. The thermal gravimetric graph indicating 4.85% weight losses of untreated sludge, while 31.09% weight losses for treated sludge up to 300 °C temperature. This ascribes the removal of moisture and volatile material available in both sludge and found to be more in treated sludge. In literature 70.5% weight losses from total sludge weight of petrochemical industry at 102 °C with activated carbon process . Further increase in temperature up to 600 °C only 5.99% weight losses untreated sludge and 68% weight losses for treated sludge was examined. This means that untreated effluent having more non-volatile material as compared to iron electrode treated wastewater. Nearly 54.57% weight losses at 731.25 °C temperature were reported for simulated industrial wastewater . The differential thermal gravimetry curve demonstrated 84 µg/min weight losses at temperature Tmax 228 °C for untreated and 0.62 mg weight losses at Tmax527 °C for combined treated sludge. The reactions seem to be exothermic and the heat evolution 4900 J/g was noted for treated samples . The decomposition was nearly completed at 800 °C for untreated sludge and 523 °C for combined treated sludge. At last temperature 1000 °C approximately 93.58% weight and 28.34% weight was found for untreated and treated sludge. Hence it can be assumed that the treated sludge contains low inorganic material as compared with untreated sludge of sugar industry wastewater .
The wastewater from sugar industry has complicated characteristics and difficult to manage up to dischargeable norms with the traditional method. At most constructive condition 85 °C working temperature, adjusted pH 8, 8Kg/m3 mass loading, and 4 h experimental time, 68.5% chemical oxygen demand and 71.2% color removal can be achieved. Treatment with electrocoagulation at optimum condition pH 7, 20 mm electrode distance, 120 min of experimental time, and 156Am−2 current density, maximum 82.5% chemical oxygen demand, and 86.5% color reduction can be achieved. The combined (thermal and electrochemical) treatment shows 98% chemical oxygen demand and 99.2% color reduction at the most optimum condition in 20 min of treatment time. The setting was 20:80 solid–liquid interfaces at 120 min of detention time. The filtration shows low cake resistance 0.451 × 10–14 and filters medium resistance 2.15 × 10–12 for combined treated sugar industry wastewater. The sludge generated having less ash contain (23.34%) and high heating value as compared to without treated sugar industry wastewater. This sludge can be mixed as construction material or used as heating purposes. This study has been proofed that single-stage treatment is not the potential to treat the wastewater up to recycling limit.
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Author acknowledge to Department of Chemical and Petroleum Engineering, UIE, Chandigarh University Mohali (Punjab) for providing lab facilities
Conflict of interest
The author declares no conflicts of interest.
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Sahu, O. Deduction of Organic and Inorganic Pollutant from Sugarcane Processing Plant Effluent by Thermal-oxidation and Electro-oxidation Processes in Batch Experiment. Chemistry Africa (2020). https://doi.org/10.1007/s42250-020-00167-y
- Chemical salt
- Thermal treatment