Abstract:
Coagulation is the most common way to remove the bulk of natural organic matter
(NOM) from moorland source waters during drinking water treatment. Deteriorating
water quality and tightening regulations have created the need for more effective
treatment options. A review of the literature identified a range of enhanced treatment
options that are available for NOM removal. A novel highly charged Zr coagulant
(referred to as Zr-OCl) has also been proposed to enhance NOM removal. The aim of
this thesis was to evaluate the use of Zr-OCl as a coagulant in continuous operation at
pilot scale by benchmarking the performance of Zr-OCl against a conventional ferric
coagulant (referred to as Fe-Coag). The potential use of Zr-OCl in a blend with Fe-Coag
was also investigated. The removal of NOM, turbidity and disinfection by-product
(DBP) precursors as well as the zeta potential and the strength of flocs was measured.
The characteristics of Zr were related to the mechanisms of the coagulation process. It
was clear that Zr-OCl could remove more NOM than Fe-coag displaying 7-10 %
increased removal of dissolved organic carbon (DOC), 6-10 % increased removal of
absorption of ultraviolet light at 254 nm (UV254), 31- 62 % increased turbidity removal
and 23-38 % lower THM-FP. Zr-OCl also added more charge to the system and
operated over a wider zeta potential range which explained the increased removal. The
higher charge and wider operational range was explained by the characteristics of Zr
found in the literature review. The Zr-OCl flocs were stronger than the Fe-Coag flocs
resulting in less breakage during solid-liquid removal. When different blends of Zr-OCl
and Fe-Coag were used there was an incremental increase in performance as a result of
an increased amount of Zr in the blend for a given dose. The possible use of Zr-OCl a
coagulant was put into context by comparing it to the other treatment options
investigated in the literature review.