Kinetics and modeling of trihalomethane precursors in lakes and reservoirs

In this study, laboratory experiments were conducted for quantification of autochthonous THMP production and characterization of THMP losses through biodegradation and photolysis. A 'yield' approach was defined to estimate autochthonous production. The yield coefficient is a function of light intensity, behaving like a first order decay with high values at low light intensities, approaching an asymptote at high irradiance. Biodegaradation experiments suggest that the THMP pool is divided into biologically labile and refractory (or slightly labile) fractions. Most (∼70%) of the THMPs produced by algae are highly labile and much of the balance is slightly labile. The labile THMP content of allochthonous inputs is about 15--20% with the balance being refractory. Biodegradation rates of labile THMPs are on the order of 0.1--0.2 d-1, approximately two orders of magnitude greater than those for photolysis.;An assessment of autochthonous and allochthonous inputs of THMPs was conducted for NYC reservoirs. Allochthonous THMP loads were calculated as the product of flow and tributary THMP concentration. Allochthonous THMP unit areal loads (UALs), averaged over the April--October period, ranged from 0.16 to 1.71 mg THMP·m-2·d-1 . Areal autochthonous production ranged from 2.5 to 38.3 mg THMP·m -2·d-1 for the April--October period. A simpler, chlorophyll-based screening model was derived based on the observed correlation between chlorophyll concentration and autochthonous THMP production in NYC reservoirs. The screening model was applied in the evaluation of relative contributions of autochthonous input to THMP pool for NYC reservoirs. It was found that in the seven NYC reservoirs, autochthonous production accounted for 2--76% of the THMP loading, averaged over the April--October period. The contribution of internal sources was significantly less for the three oligotrophic reservoirs (averaging 8%) than for the mesotrophic (averaging 50%) or eutrophic (65%) systems.;An analysis was conducted to evaluate economically in-reservoir THMP remediation through watershed phosphorus loading control for Cannonsville Reservoir. A 34-year period model simulation demonstrates that watershed phosphorus control is an effective approach for controlling reservoir THMP levels. A comparison was made in the effectiveness and costs between in-reservoir THMP remediation and in-plant THMP removal techniques. The latter ones represent a costly choice. In-reservoir THMP remediation would bring savings in treatment costs. For Cannonsville Reservoir, every dollar consumed in watershed phosphorus control produces a saving of 0.84, 0.23 and 0.16 dollar in enhanced coagulation, nanofiltration and GAC adsorption, respectively, at a treatment capacity of 520 mgd.