THESIS
2022
1 online resource (xxi, 152 pages) : illustrations (chiefly color), color map
Abstract
At the Stonecutters Island Sewage Treatment Works (SCISTW) of Hong Kong
Harbour Area Treatment Scheme (HATS), chlorination is applied to disinfect
the Chemically Enhanced Primary Treated (CEPT) sewage before discharge to
protect the marine environment and surrounding beaches. A high concentration
chlorine solution (in sodium hypochlorite form; ≈ 10
5 mg/L) is injected into
the CEPT effluent through multiple dense jets. Field observations have revealed
unexpected large amount of chlorine consumption (around 70 - 80%) by contaminants
in CEPT sewage before inactivating pathogenic microorganism. In view
of the importance of sewage disinfection to the environment, it is essential to
study the optimization strategies of chlorine disinfection dosage at SCISTW.
In this study, several important a...[
Read more ]
At the Stonecutters Island Sewage Treatment Works (SCISTW) of Hong Kong
Harbour Area Treatment Scheme (HATS), chlorination is applied to disinfect
the Chemically Enhanced Primary Treated (CEPT) sewage before discharge to
protect the marine environment and surrounding beaches. A high concentration
chlorine solution (in sodium hypochlorite form; ≈ 10
5 mg/L) is injected into
the CEPT effluent through multiple dense jets. Field observations have revealed
unexpected large amount of chlorine consumption (around 70 - 80%) by contaminants
in CEPT sewage before inactivating pathogenic microorganism. In view
of the importance of sewage disinfection to the environment, it is essential to
study the optimization strategies of chlorine disinfection dosage at SCISTW.
In this study, several important aspects of chlorine dosage optimization at SCISTW
are investigated. Firstly, the chlorine demand by dominating chlorine consumption
constituents (ammonia nitrogen and organic nitrogen) in the CEPT sewage
has been systematically studied in chlorine jet mixing with ambient sewage coflow
(ammonia nitrogen, organic nitrogen and CEPT sewage) in a laboratory experimental
flume. This is the first time that the chlorine demand by (i) ammonia
nitrogen; (ii) organic nitrogen and (iii) real CEPT sewage in a reacting chlorine jet mixing with ambient sewage coflow have been studied. A total number
of 128 runs have been performed. The chlorine demand by ammonia nitrogen
and organic nitrogen highly depends on the source chlorine concentration and
the jet mixing conditions in laboratory flume tests. The largest chlorine consumption
by breakpoint chlorination is approximately 11% of dosed chlorine at
a source chlorine concentration of 9,500 to 12,500 mg/L in laboratory experimental
flume. The largest chlorine consumption by dissolved organic nitrogen is
approximately 27% of dosed chlorine at a source chlorine concentration of 10,000
mg/L in laboratory experimental flume. The chlorine demand measurements in
jet mixing with ammonia nitrogen coflow in laboratory flume can be explained
by jet dilution as predicted by a well-established jet model - VISJET.
To overcome the time lag of chlorine dosing system and improve the treatment
efficiency for chlorine disinfection dosage control, an autoregressive (AR
(4)) model
to forecast sewage flow (with 30 mins lead time) in SCISTW has been developed.
It is found that the deviation of the predicted flow from the actual flow is in
general less than 5% or 1.5 m
3 /s.
The potential of automatic enzymatic measurements (as a surrogate) of E.coli
concentration using a ColiMinder has also been studied.
Post a Comment