Elsevier

Chemosphere

Volume 253, August 2020, 126652
Chemosphere

Treatment of dairy industry wastewater by combined aerated electrocoagulation and phytoremediation process

https://doi.org/10.1016/j.chemosphere.2020.126652Get rights and content

Highlights

  • Aeration improved the performance of electrocoagulation.

  • Al–Fe electrode combination found effective for diary wastewater treatment.

  • 97% COD removal by combined electrocoagulation and phytoremediation process.

Abstract

As dairy industries has been emerged as one of the most rapidly developing industry in both small as well as large scale, the volume of effluent generated is also very high. In the present study, aerated electrocoagulation combined with phytoremediation treatment was conducted in dairy industry wastewater. Electrocoagulation was performed with aluminium and iron electrodes and effect of various operating parameters such as electrode combination, pH, and voltage were tested. Electrocoagulation was found effective at neutral pH and its efficiency increased with increase in applied voltage. The maximum COD removal efficiency of 86.4% was obtained in case of Al–Fe electrode combination with aeration at 120 min reaction time, initial pH 7, voltage 5 V. Significant growth of Canna indica was observed in electrocoagulation treated wastewater compared to raw dairy wastewater. COD removal of 97% was achieved when combined electrocoagulation and phytoremediation process was used. Thus, it proves to be a proficient method for the treatment of dairy industry wastewater. In addition to the above, bacterial toxicity tests were performed to investigate the toxic nature of wastewater and the results showed that both treated and untreated wastewater favoured bacterial growth.

Introduction

The industries which generate huge volume of effluents includes the food processing, textile pulp and paper, distilleries etc. (Valta et al., 2015; Chowdhary et al., 2018). Among the food processing industries, dairy industry is of major concern as it generates 0.2–10 L of wastewater per litre of processed milk (Tchamango et al., 2010; Bazrafshan et al., 2013; Martín-Rilo et al., 2015). The dairy industry wastewater is characterised by high biological oxygen demand (BOD), chemical oxygen demand (COD) and nutrients level (Tchamango et al., 2010; Martín-Rilo et al., 2015; Ahmad et al., 2019). In most of the cases, the wastewater is disposed in the environment without any treatment which may lead to several severe problems such as surface and ground water pollution, eutrophication due to the presence of nitrates and phosphates that increases human health risk and ecosystem imbalance. Therefore, treatment of dairy industry wastewater becomes very important not only for the environment but also to fulfil the water requirement for a dairy industry (Tchamango et al., 2010; Sharma, 2014; Rad and Lewis, 2014; Jagadal et al., 2017; Ahmad et al., 2019). There are many biological treatment processes available for dairy industry wastewater including anaerobic sludge blanket reactors, anaerobic biofilm reactors, trickling filters, sequencing batch reactor, aerated lagoons, activated sludge process, anaerobic filters, etc. (Bazrafshan et al., 2013; Karadag et al., 2015a, 2015b; Kolev Slavov, 2017). The aerobic biological process involves higher energy requirement whereas anaerobic treatment processes results in poor nutrient reduction and also needs further treatment of the effluent (Bazrafshan et al., 2013).

On the other hand, electrocoagulation (EC) process has become a prominent method to treat water as well as wastewater as it includes the benefits of coagulation, floatation and electrochemistry (Moussa et al., 2017; Syam Babu et al., 2019a). It is an alternative chemical method for wastewater treatment (Smoczynski et al., 2013). The three important phenomena which takes place during an EC process are electrolytic reactions on the surface of the electrode (commonly aluminium or iron), coagulant formation in the water medium and adsorption of colloidal or soluble pollutants with the aid of coagulant and separation by flotation or sedimentation due to small hydrogen bubbles generated by the cathode which facilitates the segregation of particles in the wastewater (Rodríguez et al., 2010). EC treatment has emerged as an environment-friendly treatment process of wastewater with minimal sludge generation, requires no additional chemical additives and also has minimum footprint without effecting the efficiency of the treatment process (Valero et al., 2011; Sahu et al., 2014; Aswathy et al., 2016). It has many other advantages such as easier installation and maintenance, lower reaction and retention time, odourless treatment and can be adopted for the treatment of variety of wastewaters. In the recent years, EC has been widely employed for the treatment of poultry slaughterhouse wastewater (Bayar et al., 2014), winery wastewater (Kara et al., 2013), molasses water (Tsioptsias et al., 2015), arsenic contaminated water (Nidheesh and Singh, 2017; Syam Babu and Nidheesh, 2020), textile effluents (Ghanbari and Moradi, 2015), tannery wastewater (Deghles and Kurt, 2016; van Genuchten et al., 2016; Eryuruk et al., 2018), crude vegetable oil refinery wastewater (Preethi et al., 2020), mixed industrial wastewater (Nidheesh et al., 2020), oily wastewater from locomotive wash facilities (Sravanth et al., 2020), food processing industry wastewater (Zhao et al., 2014) and dairy industry wastewater (Bazrafshan et al., 2013; Smoczynski et al., 2013; Aitbara et al., 2016).

Recent studies by our group reported that addition of air during electrocoagulation process has significant effect on process efficiency (Kumar et al., 2018). Kumar and co-workers (Kumar et al., 2018) conducted electrocoagulation experiments for the composite wastewater with and without the supply of additional oxygen and found more colour and COD reduction with the supply of additional oxygen. The same was reported by Syam Babu et al. (2019b) for the remediation of arsenite contaminated water. In the present study, iron and aluminium electrodes and also its combinations (Al–Al, Al–Fe, Fe–Al and Fe–Fe) with and without aeration were studied to obtain the maximum efficiency under various operating parameters including electrode combination, initial pH and applied voltage.

Bioremediation is a set of technologies used for the reduction of in-situ and ex-situ concentration of wide range of organic as well as inorganic pollutants by biochemical processes with the aid of selective species of plants and microorganisms (Ferniza-García et al., 2017). Phytoremediation is a type of bioremediation process in which selective plant species are used directly to separate, remove, brace, and/or degrade contaminants in the soil and groundwater (Laghlimi et al., 2015; Ribeiro et al., 2016). It emerges to be a low-cost, aesthetically pleasing, eco-friendly and sustainable technology for the removal of organic as well as inorganic contaminants (Kang, 2014; Khandare and Govindwar, 2015; Rezania et al., 2015). This technology has already showcased its efficacy in remediating domestic wastewater as well as different industrial effluents (Darajeh et al., 2014; Akinbile et al., 2016; Kumar et al., 2019). It is more effective when the concentration of the contaminants range from low to medium whereas higher concentration hinder the growth of plants and microorganisms (Laghlimi et al., 2015). Selection of plant species depends on atmospheric condition, availability, nature and concentration of contaminants (Huang et al., 2017). Canna indica also known as Indian shots is a perennial plant with long stems and large leaves. It is a wetland species and successfully used for the remediation of domestic wastewater and pesticide contaminated water (Cheng et al., 2007; Cui et al., 2010). Until now, it has not been employed for the treatment of wastewater from dairy industries. Hence, this plant was selected for the phytoremediation process.

Wastewater discharged from the industries may contain different types of toxic compounds exerting harmful effects on the living organisms specifically microbial community since most of the toxicants can sometimes leads to death. Negligible reports are available on the toxicity of dairy industry wastewater. Hence, it is essential to study the toxicity of compounds present in the dairy industry wastewater on bacterial population. Growth of aerobic bacteria seems to be a rapid, sensitive and cost effective parameter to evaluate the toxicity of a compound.

In our study, the significance of aerated electrocoagulation combined with phytoremediation for the treatment of wastewater generated from dairy industry was investigated. Moreover, bacterial toxicity assays were performed to assess the toxicity of dairy industry wastewater.

Section snippets

Dairy wastewater

The wastewater was collected from a food processing industry located in Maharashtra. The samples were collected from the outlet of the processed water without filtration or pH correction. Grab sampling method was adopted for the sample collection and the collected samples were refrigerated at 4 °C to prevent further biological degradation.

Chemicals

All the chemicals used in this study were of analytical grade. Sodium hydroxide, sulphuric acid (98% pure) bought from Merck was used for pH correction

Characteristics of wastewater

The characterization of wastewater was done as per the standard methods (APHA, 2012). Table 1 shows the determined values of wastewater. pH of the wastewater was 5.87 and the turbidity was found to be 617 NTU. BOD and COD of the wastewater were determined to be 4480 and 5600 mg L−1 respectively with a BOD to COD ratio of 0.8. High BOD/COD ratio is an indication for suitability of the wastewater for biological treatment. At the same time, higher suspended solid concentration (4.53 g L−1) is not

Conclusions

Combined electrocoagulation-phytoremediation process was found to be a promising technology for treating dairy industry wastewater. The maximum COD removal efficiency of 86.4% was obtained with Al–Fe combination for aerated EC experiments for a reaction time of 2 h. The optimum initial pH obtained was 7 and the applied voltage was found to be 5 V as it contributed the maximum removal efficiency. Phytoremediation of treated as well as untreated wastewater was performed successfully with Canna

CRediT authorship contribution statement

J. Akansha: Formal analysis, Data curation, Validation, Writing - original draft. P.V. Nidheesh: Conceptualization, Methodology, Formal analysis, Supervision, Writing - original draft, Writing - review & editing. Ashitha Gopinath: Formal analysis, Supervision, Writing - original draft, Writing - review & editing. K.V. Anupama: Investigation, Writing - original draft. M. Suresh Kumar: Supervision, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

Authors are thankful to the Director, CSIR-NEERI, Nagpur for providing encouragement, and kind permission for publishing the article. Authors are also thankful to Dr. Kishore Malviya, SMS Envocare Limited, Nagpur for supporting the present work.

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