Sequential treatment of paper and pulp industrial wastewater: Prediction of water quality parameters by Mamdani Fuzzy Logic model and phytotoxicity assessment
Graphical abstract
Introduction
Wastewater produced from pulp and paper industry during subsequent industrial operations is significantly deteriorating the quality of environment. This industry is water demanding and ranks third in the world in terms of freshwater usage after primary metal and chemical industries (Savant et al., 2006, Kamali and Khodaparast, 2015) and being categorized among seventeen most polluting industries by Central Pollution Control Board of India (Rajwar et al., 2017). According to a survey report, about 3 billion m3 wastewater from paper and pulp industry needs to be managed each year (FPAC, 2009). A huge amount of wastewater is produced during pulping and bleaching stages involved in the manufacturing of paper. At pulping stage, wood pieces are boiled at very high temperature and pressure in the presence of chemicals to break up lignin and hemicelluloses (Singh and Thakur, 2006). Bleaching chemicals are injected into pulp during bleaching process and the resulting mixture is washed with resin acid, chloroform, dioxins, chlorate, chlorinated hydrocarbons, phenols and furans (Buzzini and Pires, 2007). These compounds deteriorate the water quality when are directly discharged into the environment posing serious threat to various ecosystems (Flohr et al., 2012).
In Pakistan, there are twenty-six paper manufacturing units involved in the production of various types of papers and boards, having an annual production capacity of 575 thousand tons (Akhtar et al., 2013). The wastewater produced from these units contains higher concentrations of nitrogenous compounds, total suspended solids (TSS), adsorbable organic halides (AOX), lignin compounds with their derivatives and chlorinated compounds characterized by high pH, chemical oxygen demand (COD) and biological oxygen demand (BOD) (Buzzini and Pires, 2007). Various treatment options are available for the treatment of such types of contaminated wastewaters. Conventionally, the main wastewater treatment processes involved in paper and pulp industry are primary clarification (floatation or sedimentation), secondary processes (anaerobic digestion or activated sludge process) and tertiary treatment (ultrafiltration/membrane processes) (Ksibi et al., 2003). The physico-chemical methods are very expensive, take large space to remove only higher molecular weight chlorinated compounds, lignin, color, COD and TSS (Savant et al., 2006). This process of treatment results production of metal-OH toxic sludge, and causes greenhouse gases emission (Ashrafi et al., 2013), which ultimately reduces the efficiency of process (Toczyłowska-Mamińska, 2017). To overcome these limitations, aerobic and anaerobic treatments are applied.
Aerobic process is efficient for treatment of wastewater, for instance, Rajwar et al. (2017) reported that co-inoculation of Nigrospora sp. and Curvularia sp. fungi removed BOD, COD and lignin by 86, 80 and 76%, respectively. On other hand, anaerobic process is efficient at reducing COD and color while inefficient at removing lignin contents for paper and pulp wastewater (Kariminejad et al., 2017). Therefore, the combination of both treatments (sequential) can overcome the difficulty in biodegradation of contaminants in wastewater (Singh and Thakur, 2006, Ashrafi et al., 2015). In literature, sequential treatment (anaerobic/aerobic) has been tested but for a short duration of 20 days which resulted in 58% removal of AOX and 91% removal in COD of wastewater released from Dalaman SEKA Pulp and Paper Industry (Tezel et al., 2001). Moreover, sequential treatment has also been found superior due to the less use of energy, removal of nutrients and other chemicals like antibiotics (Christgen et al., 2015, Gao et al., 2018).
Wastewater treatment processes are often complex and need to simulate the processes to find suitable operational control of the system under consideration (Lee, 2004; Nadiri et al., 2018a). Previous studies had focused on simulation of wastewater treatment processes and uncertainty of water quality parameters during these processes (Mingzhi et al., 2009, Yue et al., 2014). The sequential wastewater treatment triggers the complexity of these processes and simulation of them is vital to control the system which indicates that preparing capable models to control behavior of a wastewater treatment system is challenging. Mamdani Fuzzy Logic (MFL) is capable to handle uncertain water quality parameters and complex processes (Nadiri et al., 2017a, Sadeghfam et al., 2016). Therefore, it could be appropriate technique to simulate the sequential wastewater treatment process.
The use of treated wastewater for irrigation is of growing interest due to the shortage of good quality water. Untreated effluents from paper industry have been found to increase pH, electrical conductivity (EC), organic carbon (OC), exchangeable Na and K of the nutrient deficient soil (Oguntade et al., 2015). Moreover, improper use of untreated industrial effluent can reduce crop growth and alter the natural characteristics of soil due to the presence of contaminants (Niroula, 2003). Treated paper and pulp wastewater is beneficial in improving soil physico-chemical properties of soils such as water holding capacity, organic matter, soil structure and bulk density (Rashid et al., 2006).
The number of studies either have used aerobic and anaerobic processes to treat industrial wastewater (Kamali and Khodaparast, 2015, Rajwar et al., 2017, Kariminejad et al., 2017) or have predicted wastewater quality parameters using various simulation models (Ashrafi et al., 2013, Asadi et al., 2014, Nadiri et al., 2018a, Nadiri et al., 2018b). However, this study is unique because it has reported paper and pulp wastewater characterization by sequential treatment (40 days) associated with simulating treatment process and predicting water quality parameters by MFL model and subsequently addressed the effect of treated wastewater on Brassica growth. Based on these assumptions, present study was conducted with the following objectives to: i) assess the physico-chemical characteristics of paper and pulp industrial wastewater, ii) determine the effects of sequential, aerobic and anaerobic treatments on quality of paper and pulp industrial wastewater, iii) simulate the wastewater treatment process by MFL model and iv) phytotoxicity assessment of treated wastewater on the growth of Mustard (Brassica campestris) plant.
Section snippets
Wastewater collection
Wastewater was collected from Lahore industrial area at the outlet of paper and pulp mill factory, taken in a clean plastic cane having capacity of 30 L liquid. The wastewater was stored at 4 °C before it was transferred to the Laboratory of Department of Environmental Sciences, PMAS-Arid Agriculture University, Rawalpindi, Pakistan.
Wastewater treatment setup
Sequential, anaerobic and aerobic treatments were used for the treatment of paper and pulp industrial wastewater (Fig. 1). Aerobic treatment was carried out in a
Wastewater characteristics
Physico-chemical properties of paper and pulp industrial wastewater were analyzed before starting the treatment process and compared with National Environmental Quality Standards (NEQS, 2000) and Thailand Environmental Protection Agency (Thailand-EPA). Results revealed that TSS and COD were almost 3.5 times more than the values recommended by NEQS-Pak (Table 1). The effect of treatments on different physico-chemical properties of treated wastewater and the impact of treated water on mustard (
Discussion
Present study found that paper and pulp industrial wastewater contained number of hazardous chemicals, especially the values of TSS, COD and BOD are higher than standard set by Pakistan and Thailand (Table 1). Our results are corroborated the finding of Kariminejad et al. (2017) that reported high amount of salts, turbidity, BOD and COD in paper and pulp wastewater due to the presence of organochlorine compounds produced during different processes of pulping and bleaching processes via the
Conclusions
Wastewater treatment systems especially the biological ones have become hotspots for environmental sustainability while the use of treated industrial wastewater for irrigation of crop plants has become the need of the hour due to severe shortage of good quality water in coming decades. Keeping in view, the current study investigated the comparative effectiveness of different biological treatment for the removal of TDS, TSS, turbidity, BOD and COD from paper and pulp industrial wastewater and
Conflicts of interest
Authors declare no conflict of interest.
Acknowledgment
This research work was funded by Higher Education Commission of Pakistan under grant no. 21–576/SRGP/R&D/HEC/2014.
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