An Innovative Process for the Treatment of High Loaded Surface Waters for Small Communities

Article excerpt

Abstract: Treatment trials have been realized with a new compact process in order to meet the drinking water regulation newly implemented in the province of Quebec. This process is especially designed for the supply of small communities. It combines complementary treatments operated by a centralized computer: ozonation, membrane filtration, and biological filtration, thus reducing operation to basic tasks. The process functioned very well for the period under review, in spite of extreme conditions met: cold water and constant fluctuation of the raw water quality. The process considerably lowers the contents of organic compounds (TOC, DOC, and color), the turbidity, the chlorine demand, and the concentrations of trihalomethane precursors present in the raw water. For this specific application, the backwash wastewaters may be mixed and discharged directly into a river nearby.

Key words: drinking water, small communities, ozonation, membrane filtration, biological activated carbon, turbidity, trihalomethane precursors, TOC.

Resume: Des essais de traitement ont ete realises dans le cadre de l'accreditation d'un nouveau procede par le Comite sur les technologies de traitement en eau potable du gouvernement du Quebec. Le procede teste est compact et il est concu specialement pour alimenter les petites communautes. Il combine differentes etapes de traitement complementaires (ozonation, filtration sur membrane et filtration biologique) et commandes par un systeme de controle automatique. Le procede a tres bien fonctionne pendant la periode de suivi, malgre les conditions extremes rencontrees : eaux froides et fluctuation constante de la qualite de l'eau brute a traiter. Le procede abaisse considerablement les teneurs de composes organiques (COT, COD et couleur vraie), la demande en chlore, les concentrations de precurseurs de trihalomethanes (SDS-THM) et la turbidite presentes dans l'eau brute. Dans le cas experimente, les eaux de lavage du tamis, des membranes et des unites de filtration peuvent etre melangees et rejetees directement dans le milieu environnant.

Mots cles: eau potable, petites communautes, ozonation, membrane, traitement biologique, turbidite, precurseurs de trihalomethane, COT.

Introduction

Stricter regulations concerning drinking water quality have been implemented in Canada. Small communities need to upgrade their existing drinking water treatment plants in order to respond to these new regulations. They necessitate compact treatment plants efficient and easy to operate. Premanufactured compact treatment plants are easily transported in a shipping container, which minimize construction costs, and they do not necessitate large on-site infrastructures.

In the province of Quebec, the new regulation requires that the treated water has trihalomethane levels below 80 [micro]g/L, that turbidity of the treated water is low (below 0.1 nephelometric turbidity units, NTU, for membrane treated water) and that high removal of pathogen microorganisms occurs (the treated water must not contain pathogen organisms or indicator organisms of a fecal contamination, such as fecal coliforms, Escherichia coli, enterococcus bacteria, and coliphage viruses; Government of Quebec 2001).A new compact process must aim to meet this regulation. It has to combine complementary treatments removing particles, trihalomethane precursors, and microorganisms. The combination of ozone (inactivating pathogens and oxidizing trihalomethane precursors), membrane filtration (removing particles), and biological filtration (reducing chlorine demand and removing biodegradable organic matter) seems to be appropriate to achieve these objectives. The coupling of ozonation and biological activated carbon filtration is very effective to remove trihalomethane precursors (Niquette et al. 1999). The addition of a clarification step would help to remove pathogens and organic matter, but it needs the addition of coagulants and it produces sludge. …