Abstract
In this study, the effect of pre-treatment methods was investigated for membrane treatment of pistachio processing wastewater (PPW). Chemical coagulation, electrocoagulation, and electrooxidation processes were tested as the pretreatment methods to understand the effect of pretreatment on membrane performance. Alum (Al2(SO4)3·18H2O), iron (III) chloride (FeCl3·6H2O) and iron(II) sulfate (Fe(SO4)·7H2O) were used as coagulant and anionic polyelectrolyte was used as flocculant. Al–Al and Fe–Fe electrode pairs were used in the electrocoagulation experiments while platinum (Pt), boron doped diamond (BDD), and graphite were used in the electrooxidation experiments. UP150, NF270, and NF90 were used as the membranes. Chemical oxygen demand (COD) and total phenol removal efficiencies from wastewater were determined by considering membrane flux. For chemical coagulation experiments, the highest COD removal efficiency was determined as 44.9% for Al2(SO4)3.18H2O at 1000 mg/L when the wastewater pH value was 8.0. However, the highest total phenol removal efficiencies were obtined as 62.5% at 4000 mg/L for FeCl3.6H2O at pH 8. For electrocoagulation experiments, the highest COD and total phenol removal efficiencies were determined as 63.9% at pH 4.0 and 74.2% at pH 7.0, respectively, for 100 A/m2 current density when aluminum electrode pairs were used. For electrooxidation experiments, the highest COD and total phenol removal efficiencies were determined as 61.2% at pH 4.0 and 83.1% at pH 10, respectively, for 200 A/m2 current density when BDD-Pt electrode pairs were used. Raw PPW and pre-treated PPW with chemical coagulation, electrocoagulation, and electrooxidation processes were progressively further treated with ultrafiltration (UP150) and nanofiltration (NF270, NF90) membranes to improve COD and total phenol removal efficiencies. The results showed that the permeate of NF90 membrane supplied the highest COD (96.0%) and total phenol removal (97.5%) efficiencies for the raw wastewater. However, COD and total phenol removal efficiencies were determined as 98.6% and 100% for electrocoagulation + NF90, 97.9% and 100% for electrooxidation + NF90, 96.6% and 100% for chemical coagulation + NF90, respectively. The steady-state fluxes for NF90 membranes were 2.9, 7.0, and 8.6 L/m2h after chemical coagulation, electrooxidation, and electrocoagulation, respectively. The results depicted that electrocoagulation and electrooxidation were the most suitable pre-treatment methods for water recovery using NF90 membrane.
Highlights
The effect of pre-treatment methods was investigated for membrane treatment of pistachio wastewater
Al-Al and Fe-Fe electrode pairs were used in the electrocoagulation experiments while platinum, boron doped diamond, and graphite were used in the electrooxidation experiments
Chemical oxygen demand (COD) and total phenol removal efficiencies from wastewater were determined by considering membrane flux
Summary
The importance of water, which is one of the most basic necessities of life on earth, continues to increase due to population growth, climate change, urbanization, and the spread of irrigated agriculture (Kılıç, 2020). In the 2019 and 2020 reports of the World Economic Forum, water scarcity was stated as one of the biggest global risks in terms of potential impact for the 10 years (Marsh and McLennan, 2020) For this reason, it is of great importance to treat and reuse the wastewater generated after use for human consumption and after industrial activities. Pistachio processing plants are one of the industries with intense water consumption and high pollution. The soft organic hull around the pistachios is softened with water and separated from the pistachio During this process, 8–10 L of water is used for 1 kg of pistachios. Considering the production data in Turkey, this situation necessitates the treatment of approximately 850,000 m3 of wastewater from pistachio processing plants per year
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