Upgrading secondary wastewater plant effluent by modified coagulation and flocculation, for water reuse in irrigation

Ali Nikoonahad,Eghbal Ehsanzadeh,Mohammad Hassan Ehrampoush,Mohammad Miri,Mohammad Taghi Ghaneian

doi:10.2166/wrd.2016.049

Abstract

In this study, the feasibility of using coagulation, flocculation, and sedimentation (CF-S) for advanced treatment of secondary effluent released from the Yazd Intermittent Cycle Extended Aeration System was investigated. Four coagulants including ferric chloride (FeCl3), polyaluminum chloride (PAC), ferrous sulfate (FeSo4), and potassium ferrate (K2FeSo4) along with Gflog C-150 as flocculant polymer were used. In this study, returned chemical sludge was considered as a modification. Preliminary CF-S processes showed that FeSO4 and K2FeO4 had low removal efficiencies. Thus, these two coagulants were abandoned and CF-S processes were continued only with PAC and FeCl3 coagulants which had higher efficiencies in the removal of biological oxygen demand (BOD5), chemical oxygen demand (COD), total suspended solids (TSS), and turbidity. Removal efficiency was higher when half of the chemical producing sludge was returned as compared with using both coagulants simultaneously along with 2 mg L−1 of C-150 as flocculant. In the optimum dosage, when half of PAC and FeCl3 sludge were returned, the volume of produced sludge was reduced by 40% and 28%, respectively, as compared without returned sludge. For the PAC coagulant in the optimum dosage with half of the sludge returned, all 2012 EPA standards of irrigation were met for both ‘processed and non-processed type’ agricultural crops.

Highlights

The city of Yazd, with a mean annual precipitation of 60 mm, is known as one of the most arid desert regions in Iran, where water shortage is considered to be a critical challenge
When half of the sludge was returned to CF-S processes in polyaluminum chloride (PAC) optimum dosages, all recommendations set by Yazd Water and Wastewater Company and 2012 EPA standards of irrigation were met for both ‘processed and non-processed type’ agricultural crops
Using PAC and FeCl3 each with half of the produced sludge as a modification or each with 2 mg LÀ1 of C-150 polymer, resulted in higher removal efficiencies of BOD5, chemical oxygen demand (COD), total suspended solids (TSS), and turbidity compared with using each coagulant alone

Summary

Introduction

The city of Yazd, with a mean annual precipitation of 60 mm, is known as one of the most arid desert regions in Iran, where water shortage is considered to be a critical challenge. Water resources shortage, and increasing rate of conversion of water into wastewater due to population growth have led to serious consideration of water reuse. Reclaimed water can be used in different sectors, such as industry, recreation, and irrigation. The reuse of water has created great motivation to use innovation technology for upgrading wastewater effluent regarding agricultural irrigation (Löwenberg et al ). The size of a particle could affect how fast it sinks or floats, how it interacts with other particles, as well as many other properties of interest such as its hydrodynamics, transport, and aggregation in separation processes (Aguilar et al )

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