The removal of natural organic matter (NOM) at water treatment works (WTW) is essential in order to prevent toxic compounds forming during subsequent disinfection. Coagulation and flocculation processes remain the most common way of removing NOM. The properties of the resulting flocs that form are fundamental to the efficient removal of organic material. Periods of elevated NOM loads at WTW can lead to operational problems as a result of the deterioration in floc structural quality. Assessment of floc physical characteristics can therefore be a crucial tool in order to determine and predict solid-liquid removal performance at WTW. Here the growth, size, breakage, strength, re-growth, fractal dimension and settling velocity were measured for flocs formed from a NOM rich water source. NOM floc structural characteristics were measured and evaluated over a one year period in order to monitor the seasonal variation in floc structure. The results showed that a significant improvement in floc size and strength was seen during autumn and summer months. It was subsequently shown that as the organic fraction in the floc increases the floc size, settling velocity and fractal dimension all decrease. A model was proposed showing how these changes were dependent upon the adsorption of NOM onto primary particle surfaces. A range of different chemical coagulant treatment options were applied for NOM removal and the resulting floc structure compared. Considering both floc structure and optimum NOM removal the treatment systems were of the following order (best to worst): MIEX® + Fe > Fe > Fe + polymer > Al > polyDADMAC. NOM floc re-growth was shown to be limited for all the treatment systems investigated. The practical implications of the results were: (1) The requirement for careful coagulant dosing or order to achieve optimum floc characteristics. (2) The use of a pre-treatment anionic ion-exchange stage prior to coagulation. (3) A comparison of alum and ferric based coagulants suggested the ferric coagulants gave better floc structure and improved NOM removal rates.

No description available.

No description available.

Aluminium sulphate, calcium nitrate, and two cationic polymers have been used to coagulate and flocculate dilute kaolin and latex suspensions (< 100 mg/1) in a stirred vessel. The effects of the different destabilising agents on the resulting floes have been monitored using a simple continuous optical technique based on turbidity fluctuations and the behaviour of these floes under shear conditions and the possibility of subsequent floe re-formation have been investigated. The results showed vast differences in behaviour regarding to floe breakage and re formation between the systems. For a low molecular weight, high charge polymer (A) and calcium nitrate, floe breakage was almost completely reversible. However, for aluminium sulphate, limited floe re-formation was observed on restoring previous shear conditions after breakage. For a high molecular weight polymer (B), limited floe breakage was observed. Moreover, a new automated monitoring technique based on cake and vacuum filtration has been developed to assess the filterability of floes. The technique is reliable and provides reproducible results. The results showed that polymer A was more effective in enhancing filterability than polymer B for both kaolin and latex suspensions. However, polymers do not have a significant influence on the filterability of floes if the primary particles involved have high sphericity.

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During algac blooms, coagulation is frequently unsuccessful resulting in poor flotation duc to complex algal character. 11iis thesis cxplorcs tlic link between algal character and conventional treatment and the potential for developing morc appropriatc algac trcatmcnt tcclinologics. Specifically, dissolvcd air flotation (DAF) that has bccn adaptcd by dosing cationic clicmicals to the saturator to modiry bubbic surfaccs, such that it docs not rcly on coagulation, is invcstigatcd. 1'his proccss is tcrmcd PosiDAF. Analysis of dissolved algogcnic organic mattcr (AOM) extracted from problcmatic species enabled investigation of the impact of morphology and AOM on coagulation- flocculation-flotation. Both increasing surface area and charge density of algae systcrns, werc rclatcd to increasing coagulant dcmand. Application of the appropriate coagulant dcmand ensured removal of all thrcc components - cclls, AOM and coagulant. Maintaining the zcta potential bct-%vccn -10 mV and +2 mV ensured optimum rcmoval was obtained. PosiDAF trials were conducted by dosing chemicals that had previously been shown to alter bubble charge, including co3gulant, surfactant and polymer, to the saturator. Coagulants were unsuitable for use in PosiDAF as they did not remain at the bubble surface. Highly hydrophobic, cationic surfactants were observed to remove cells according to a theoretical model, such that removal improved with increasing bubbic: particic ratio and with cell size. The polymer, polyDADNIAC, achieved greater removal cfficiencies than those predicted theoretically, attributed to an increase in the swept volume of the bubble. However, polyDADMAC was sensitive to changes in AOM composition. A chemical that combines attributes of both surfactant and polyDADMAC may overcome the barriers to PosiDAF implementation.

The removal of natural organic matter (NOM) is one of the main challenges facing water utilities in both the UK and the US. As a consequence of changes in land management and an increased carbon loss from solids, a greater amount of accumulated organics is now being flushed into the aquatic environment during increased surface run-off events such as snowmelt or heavy rainfall. Furthermore, whilst traditional treatment with trivalent coagulants has proven a successful strategy in the past, operational problems are now being reported during periods of elevated organic levels in the water. These include the formation of fragile flocs, a greater particulate carryover onto downstream processes and increased disinfection by product (DBP) formation. Resin adsorption techniques were employed to fractionate the water samples into their hydrophobic and hydrophilic components. This, coupled with raw water monitoring, revealed that NOM composition and characteristics can vary, even if the total organic concentrations appear stable. In particular, hydrophobic NOM fractions contribute the majority of the charge compared to the hydrophilic fractions, and therefore exert a greater impact on coagulation conditions. Comparison across different source waters, seasons, at varying experimental scales and under varying coagulation conditions, revealed that zeta potential monitoring during coagulation takes into account the changing electrical property of the water, and in general, maintaining a value between -10<?<+3 mV will result in low and stable residuals. A similar operational zeta potential range exists for clarification processes, although the zeta potential value at the positive threshold is influenced by the hydrophobic NOM content, such that the range is extended as the specific UV absorbance (SUVA) value of the raw water decreases. Whereas the hydrophilic concentration was found to control the achievable dissolved organic carbon (DOC) residual, attributed to a negligible charge density and poor coagulant-interactions. Consequently, the key finding of this study is that raw water characterisation coupled with zeta potential monitoring will provide a straightforward guide to the mechanistic understanding of treating NOM rich waters.

Ferrate is believed to have a dual role in water treatment, both as oxidant and coagulant. Few studies have considered the coagulation effect in detail, mainly because of the difficulty of separating the oxidation and coagulation effects. This study aims to evaluate the coagulation performance of ferrate together with its oxidation effect in water and wastewater treatment processes, as it has not been studied thoroughly in previous work. The study involves laboratory-based experiments that investigate the coagulation reaction dynamically via a PDA instrument, between ferrate and a suspension of kaolin powder, and humic acid solution at different doses and pH values, and comparing the observation with the use of ferric chloride. The PDA output gives a comparative measure of the rate of floc growth and the magnitude of floc formation. The results of the tests with kaolin suspension show some similarities and significant differences in the pattern of behaviour between ferrate and ferric chloride. Ferrate demonstrated very similar coagulation characteristics to ferric chloride with regard to the influence of pH and Fe dose. However, the magnitude of floc formation with ferrate was always inferior to that with ferric chloride. The rate of floc growth with ferrate was slower and sometimes less extensive than that with ferric chloride in most cases. It was discovered that the reason for the inferior performance of ferrate was the slow formation of Fe(III) species at neutral to high pH owing to the low degradation rate of ferrate in aqueous solution at these pH values. The interaction between HA and ferrate was extensively investigated in comparison to ferric chloride in this study. The results reveal that ferrate achieved comparable or better floc formation to ferric chloride over a much broader Fe dose range. However, the degree of organics removal (DOC) was lower than ferric chloride (~5%). The results obtained from model waters containing HA were consistent with those for samples of a natural upland coloured water. Ferrate oxidation appears to increase the hydrophilic and electronegative nature of the HA leading to an extended region of charge neutralization and a consequent slightly lower HA removal compared to ferric chloride.

Seasonal periods of high rainfall have led to difficulties in removing sufficient natural organic matter (NOM) to meet trihalomethane (THM) standards, and hence better or alternative treatments are required. Typically bulk water parameters such as dissolved organic carbon (DOC) and UV absorbance at 254nm (UV254) are used to optimise treatment processes. Here the isolated fraction character and molecular weight (MW) distribution was used in conjunction with bulk water parameters to tailor process options for the treatment of humic rich waters. Three options for the removal of NOM were proposed. A staged coagulation based on the optimisation of isolated fractions. The results showed that although no significant reduction in DOC or UV254 was observed filter breakthrough was significantly reduced. Secondly a novel magnetic ion exchange process (MIEX®) for the removal of NOM was evaluated. The results showed that a combination of MIEX® and ferric reduced the THM formation potential (THMFP) by more than 50% and lower MW compounds that are known to be untreated by conventional coagulation were reduced. This option was also shown to be the most robust option for the treatment of waters with differing quality caused by seasonal changes and different catchments. Finally the addition of a range of adsorbents including carbons, hydroxides and clays to both the raw water and the isolated low MW fractions showed that an increase in DOC and UV254 removal was achievable. This was proposed as a post coagulation option during times of high organic loading. All processes provide viable options for the treatment of humic rich waters during times when current processes are being challenged and having difficulty meeting THM standards.