Total Chlorine Demand Research Articles

Characterization and mitigation of chemical oxygen demand and chlorine demand from fresh produce wash water

Washing is essential in fresh-cut produce industry to remove debris and ensure desirable shelf life. The intensive water usage during washing and water scarcity in the production regions necessitate proper water reuse and reconditioning. However, the organic compounds accumulated in the water elevate chlorine demand (CLD) and chemical oxygen demand (COD), thus complicating food sanitization and subsequent water treatment. Hereby, we examined the major sources of COD and CLD during fresh-cut produce washing, and explored the mitigation of CLD by treating select water constituents for the first time. Results showed that sugars as the predominant composition contribute to over 80% of COD in the wash water, whereas minor constituents including proteins/peptides, acids, and phenolic compounds account for over 80% of total CLD. The actual CLDs by those compounds depend highly on produce type. Moreover, while removing large molecules from the wash water led to the greatest CLD reduction for romaine lettuce, absorption of anionic molecules proved the most effective for iceberg lettuce, onion, and carrot wash water. This study suggests the possibility of mitigating CLD by more targetted and cost-effective water treatment procedures without the need for removing sugars. It also recommends prudent and product-specific design for produce sanitization and water treatments.

Impacts and interactions of organic compounds with chlorine sanitizer in recirculated and reused produce processing water.

Water conservation and economics dictate that fresh produce processors reuse/recirculate the process water. However, the ensuing accumulation of organic matter in water depletes the chlorine sanitizer required for food safety. In this study, we comprehensively investigated chemical compounds that are responsible for water quality in relation to chemical oxygen demand (COD) and chlorine demand (CLD), the two most critical factors associated with water treatment and chlorine replenishment. Simulating commercial fresh-cut wash operations, multiple batches of diced cabbage (0.3 x 0.3 cm2) were washed in the same tank of water. The major components were isolated from the wash water and analyzed by HPLC. Sugars were the predominant compounds (82.7% dry weight) and the major contributor to COD (81.6%), followed by proteins/peptides (7.3% dry weight, 5.3% COD), organic acids (6.2% dry weight, 3.6% COD), and phenolics (0.5% dry weight, 0.5% COD). By repeated time course measures, the effect of these chemicals on CLD are dependent on the chemical structure, concentration in the wash water, and their rate of reaction. Proteins/peptides accounted for about 50% of the total CLD over a 120-min period and phenolics was 21% at 5 min, but diminished with time. The contribution by organic acids and sugars increased continuously, reaching 22% and 16% of total CLD at 120 min of chlorination, respectively. Collectively, these compounds represented 86% of the CLD in cabbage wash water at 5 min and greater than 94% CLD afterwards. This is the first systematic report on the source of COD and CLD during fresh produce washing. It provides essential information for the produce processors to develop safe, effective, and economical wash water treatment/reuse and chlorine replenishment strategies.

Quantifying chlorine-reactive substances to establish a chlorine decay model of reclaimed water using chemical chlorine demands

In order to guarantee the water quality of reclaimed water in pipeline system, a chlorine bulk-decay model is required for simulation and prediction of chlorine profiles in networks. Conventional chlorine decay models of drinking water are not applicable to reclaimed water due to its complex and varying water quality. In this study, the chlorine decay of reclaimed water was investigated under different operational conditions. Based on these results, different chlorine-reactive substances (CRSs) in reclaimed water were quantified by total chlorine demand (TCD), instantaneous chlorine demand (ICD) and lasting chlorine demand (LCD), respectively. A stoichiometric model (CRS model) of chlorine decay of reclaimed water was established using ICD, TCD and reaction rate constant (k) as key independent parameters. The experimental data were fitted to the CRS model with promising results under various initial chlorine concentrations (3–10 mg-Cl2/L) and temperatures (8–35 °C). The ICD, TCD and k of different reclaimed water samples were in the range of 0.23 to 2.85 mg-Cl2/L, 1.07 to 4.73 mg-Cl2/L, and 0.04 to 4.06 L/(mg·h), respectively. Furthermore, the ICDs, TCDs and k could be determined directly by measuring the chlorine consumption at 5 min (ΔCCl,5min) and 8 h (ΔCCl,8h) after the addition of chlorine into reclaimed water, and the UV254 of reclaimed water, respectively. The relationships between ICD, TCD, k and the corresponding water quality indexes were further validated. In this way, the chlorine decay profile of reclaimed water could be predicted rapidly and precisely by measuring the ΔCCl,5min, ΔCCl,8h, and UV254 of reclaimed water.

Coagulation behavior of polyferric chloride for removing NOM from surface water with low concentration of organic matter and its effect on chlorine decay model

Polyferric chloride (PFC) was used to remove natural organic matter (NOM) from the surface water with low concentration of organic matter to evaluate coagulation behavior and floc parameters. The relationship between PFC dosages and chlorine decay was also investigated and the chlorine demand for reacting with organic compounds was estimated by a chlorine model. Under the raw water conditions, the NOM removal efficiency increased within the dosage investigated. The lower specific UV absorbance (SUVA) values were achieved in the dosage range 10–16 mg/L of PFC. Adsorption, entrapment, and complexation played important roles for PFC in removing NOM besides charge neutralization in the coagulation process. Large flocs formed with a PFC dosage of 22 mg/L were better resistant to increasing shear but showed poor recoverability. Small flocs at a PFC dosage of 3 mg/L were little influenced by the increasing shear and showed full reversibility. Coagulation treatment with 22 mg/L of PFC resulted in higher chlorine decay rate, more free chlorine residuals and less total chlorine demand in the effluent when compared to coagulation with dosages of 14 and 3 mg/L. Furthermore, minimal amount of disinfection by-products (DBPs) would be possibly produced after treatment with 22 mg/L of PFC.