Reverse Osmosis Treatment of Wastewater for Reuse as Process Water-A Case Study.

Marjana Simonič

doi:10.3390/membranes11120976

Abstract

The aim of this work was to purify mixed wastewater from three different production processes in such a manner that they could be reused as process water. The maximum allowed concentrations (MAC) from the Environmental Standards for emissions of substances released into surface water were set as target concentrations. Wastewaters contained solid particles, sodium, aluminium, chloride, and nitrogen in high amounts. Quantitatively, most wastewaters were generated in the production line of alumina washing. The second type of wastewater was generated from the production line of boehmite. The third type of wastewater was from regeneration of ion exchangers, which are applied for feed boiler water treatment. The initial treatment step of wastewater mixture was neutralisation, using 35% HCl. The precoat filtration followed, and the level of suspended solids was reduced from 320 mg/L to only 9 mg/L. The concentrations of ions, such as aluminium, sodium and chlorides remained above the MAC. Therefore, laboratory reverse osmosis was applied to remove the listed pollutants from the water. We succeeded in removal of all the pollutants. The concentration of aluminium decreased below 3 mg/L, the sodium to 145 mg/L and chlorides to 193 mg/L. The concentration of nitrate nitrogen decreased below 20 mg/L.

Highlights

Alumina (Al2O3) is considered a basic catalytic material support due to its good mechanical properties, such as high strength, chemical and physical stability, its high thermal resistance, and thermal conductivity [1]
The suspended solids’ mass concentration was too high in the washing water in boehmite production (WW2), sodium was above the maximum allowed concentrations (MAC) and aluminium was very high, measured at 33 mg/L
MAC represents the maximum allowed concentration according to the Slovenian Regulations [18]

Summary

Introduction

Alumina (Al2O3) is considered a basic catalytic material support due to its good mechanical properties, such as high strength, chemical and physical stability, its high thermal resistance, and thermal conductivity [1]. Boiler water must be softened properly before use. Without periodic water removal (blowdown), problems such as scale deposits, corrosion and embrittlement may occur [3]. A study was reported, conducted on the utilisation of a simulated boiler blowdown for incorporation into cement-based materials. The results indicate that the use of waste brine in cemented backfill applications is feasible. The phosphate addition could result in the formation of deposits such as iron phosphate. Phosphate corrosion is assumed as a significant concern in phosphate treated steam boilers [4]. After regeneration of an ion exchanger, acidic and alkaline effluents are generated, containing chlorides, sulphates, nitrates, silicates, etc

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