Adsorption/Coagulation/Ceramic Microfiltration for Treating Challenging Waters for Drinking Water Production

Rui M C Viegas,Helena Lucas,Margarida Campinas,Maria João Rosa,Rosário Coelho

doi:10.3390/membranes11020091

Rui M C Viegas, Helena Lucas + Show 3 more

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https://doi.org/10.3390/membranes11020091

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Abstract

Pressurized powdered activated carbon/coagulation/ceramic microfiltration (PAC/Alum/MF) was investigated at pilot scale for treating low turbidity and low natural organic matter (NOM) surface waters spiked with organic microcontaminants. A total of 11 trials with clarified or non-clarified waters spiked with pesticides, pharmaceutical compounds, or microcystins were conducted to assess the removal of microcontaminants, NOM (as 254 nm absorbance, A254, and dissolved organic carbon, DOC), trihalomethane formation potential (THMFP), aerobic endospores as protozoan (oo)cysts indicators, bacteriophages as viruses indicators, and regular drinking water quality parameters. PAC/(Alum)/MF achieved 75% to complete removal of total microcontaminants with 4–18 mg/L of a mesoporous PAC and 2 h contact time, with a reliable particle separation (turbidity < 0.03 NTU) and low aluminium residuals. Microcontaminants showed different amenabilities to PAC adsorption, depending on their charge, hydrophobicity (Log Kow), polar surface area and aromatic rings count. Compounds less amenable to adsorption showed higher vulnerability to NOM competition (higher A254 waters), greatly benefiting from DOC-normalized PAC dose increase. PAC/Alum/MF also attained 29–47% NOM median removal, decreasing THMFP by 26%. PAC complemented NOM removal by coagulation (+15–19%), though with no substantial improvement towards THMFP and membrane fouling. Furthermore, PAC/Alum/MF was a full barrier against aerobic endospores, and PAC dosing was crucial for ≥1.1-log reduction in bacteriophages.

Highlights

Finding resilient and cost-effective water treatment, adaptable to seasonal and to site-specific constraints, is crucial in the current climate uncertainty context of increasing limited water resources and challenging water quality requirements
11 trials with clarified or non-clarified waters spiked with pesticides, Pharmaceutical compounds (PhCs) or microcystins were conducted to assess water quality towards microcontaminants’ and natural organic matter (NOM) removal, trihalomethane formation potential (THMFP), endospores (as protozoancysts indicators) and bacteriophages, in addition to regular drinking water quality parameters
Powdered activated carbon (PAC) particle retention is crucial for an effective removal of microcontaminants, but in low-turbidity waters as those studied, there is an intrinsic coagulation difficulty due to the limiting rate of inter-particle contacts, and PAC has shown to add to this difficulty by affecting the floc formation process [22]

Summary

Introduction

Finding resilient and cost-effective water treatment, adaptable to seasonal and to site-specific constraints, is crucial in the current climate uncertainty context of increasing limited water resources and challenging water quality requirements. Diverse PhCs with potential deleterious acute and synergistic chronic health effects have been reported in surface, groundwater and even in drinking water at ng/L to low μg/L range [2,5,6], with carbamazepine, diclofenac, propranolol, and atenolol amongst the major compounds detected [7,8]. Pesticides such as atrazine, tebuconazole, diuron and dimethoate have shown critical occurrence in several water abstraction areas worldwide [9,10,11], and recent studies revealed adverse neurobehavioral effects due to prolonged exposure to pesticide mixtures, even at permitted levels [12] and higher toxicity of some pesticide metabolites compared to their parent compounds [4]. An example was the 2014 Microcystis bloom in Toledo (OH, USA) which closed the water supply for 3 days affecting 400,000 residents [13]

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