Combined Coagulation and Ultrafiltration Process to Counteract Increasing NOM in Brown Surface Water

Abstract

Membrane hybrid processes-coagulation coupled with ultrafiltration (UF)-have become a common method to comply with the legal, chemical, and microbiological requirements for drinking water. The main advantages of integrating coagulation with membrane filtration are the enhanced removal of natural organic matter (NOM) and reduced membrane fouling. With in-line coagulation, coagulants are patched into the feed stream directly prior to the membrane process, without removing the coagulated solids. Compared with conventional coagulation/sedimentation, in-line coagulation/membrane reduces the treatment time and footprint. Coagulant dosing could be challenging in raw water of varying quality; however, with relatively stable specific ultraviolet absorbance (SUVA), dosing can be controlled. Recent studies indicate that UV absorbance correlates well with humic substances (HS), the major fraction to be removed during coagulation. This paper describes and evaluates a 30-month UF pilot trial on the surface water of Lake Neden (Sweden), providing drinking water to 60,000 residents. In this study, automatic coagulant dosing based on online measurement was successfully applied. Online sensor data were used to identify the current optimal aluminium coagulation conditions (0.5-0.7 mg L −1 ) and the potential boundaries (0.9-1.2 mg L −1 ) for efficient future (2040) NOM removal. The potential increase in NOM could affect the Al dose and drinking water quality significantly within 20 years, should the current trends in dissolved organic carbon (DOC) prevail. UV absorbance, the freshness index, and liquid chromatography-organic carbon detection (LC-OCD) measurements were used to optimise the process. Careful cross-calibration of raw and filtered samples is recommended when using online sensor data for process optimisation, even in low-turbidity water (formazin nephelometric unit (FNU) < 5).

Mapping Dynamics of Bacterial Communities in a Full-Scale Drinking Water Distribution System Using Flow Cytometry

“…Historically, Kvarnagården DWTP in Varberg, Sweden had limited treatment of surface water and very high cell concentrations (7 × 10 5 cells/mL) of bacteria in the DWDS. In November 2016, the DWTP was upgraded to ultrafiltration (UF) membranes, combined with flocculation, reducing the input of bacterial cells into the DWDS and removing about 50% of natural, especially high molecular weight, organic carbon [2,21]. This upgrade was closely monitored with FCM and showed that bacterial concentrations in treated and distributed water were substantially lowered by the change in treatment processes [2].…”

Use of Acorn Leaves as a Natural Coagulant in a Drinking Water Treatment Plant

“…This process is aimed at reducing the concentration of suspended solids (SS) and non-settling colloidal particles, thus lowering turbidity and improving water quality [6]. The effectiveness of this process is known to be dependent on the nature of the particles, the type and dosage of the coagulant and the pH of the water [7,8].…”

Impact of coagulation–ultrafiltration on long-term pipe biofilm dynamics in a full-scale chloraminated drinking water distribution system

“…Treatment consisted of pH adjustment, rapid sand filtration, storage tank 1 with addition of monochloramine, followed by storage tank 2 and 3 and UV disinfection (for more details see ref. 20). In November 2016, UF was added, hereafter defined as UF start, resulting in a treatment chain of rapid sand filtration, storage tank 1, coagulation and UF, pH adjustment, storage tank 2 with addition of monochloramine, storage tank 3 and UV disinfection (Fig.…”

“…18 Bacteria in chloraminated drinking water included a community with diverse approaches to nitrogen metabolism dominated by Nitrosomonas (AOB), and Nitrospira (NOB) and accompanied by heterotrophs such as Sphingomonas 19 and these taxa were recently identified as actively conducting nitrification in diverse pipe biofilms. 13 When a drinking water treatment plant (DWTP) in Varberg, Sweden, installed an ultrafiltration (UF) facility with two-stage filtration and in-line coagulation at the primary membrane stage, 20 the new finished water (FW) contained virtually no bacteria, and less and different natural organic matter (NOM). 11 The impact of this change on the bacterial community was examined by collecting water, swabbing the surface of the biofilm, and scraping to remove deep biofilm from multiple sections of pipe in series and excavated from the operational DWDS.…”