**Determination of COD in Landfill Leachate by Ultraviolet Spectrophotometry**
UV spectrophotometric determination of COD in landfill leachate is an innovative and efficient approach that offers a faster, less toxic, and more cost-effective alternative to traditional methods. The key characteristics of landfill leachate include high chemical oxygen demand (COD), with values reaching up to 80,000 mg/L, along with complex organic compositions, color, and suspended solids. If not properly treated, the discharge of such waste can lead to severe environmental pollution, making its treatment a critical concern.
The conventional method for COD determination, the potassium dichromate method, is reliable but involves tedious procedures, high reagent consumption, and the use of toxic mercury sulfate, which leads to secondary pollution. Therefore, there is a growing need for a simpler, more sustainable, and accurate method suitable for batch analysis of COD in water samples.
Ultraviolet (UV) spectrophotometry operates in the wavelength range of 200–400 nm and is particularly effective for analyzing compounds with unsaturated bonds or conjugated systems, which are commonly found in landfill leachate. Since most of the components in leachate have these properties, UV absorbance can serve as a comprehensive indicator of organic pollution. By measuring UV absorbance at specific wavelengths, it is possible to estimate COD without the need for extensive chemical procedures, reducing both time and cost.
In this study, we collected landfill leachate from a regulation tank without filtration and measured the UV absorbance directly using a UV-1200 spectrophotometer. Simultaneously, the COD was determined using the standard method. A linear regression model was established between UV absorbance and COD values to evaluate the correlation.
**1. Experimental Setup**
1.1 **Instruments and Reagents**:
- UV-1200 spectrophotometer (Meifang, China)
- 1 cm quartz cuvettes
- Distilled water
1.2 **Methodology**:
The leachate sample was diluted with distilled water, and absorbance was measured at 254 nm using a 1 cm cuvette. The COD was also determined using the national standard method for comparison.
**2. Results and Discussion**
2.1 **Absorption Wavelength Selection**:
A full scan from 200–400 nm was conducted on a leachate sample with a COD of 1814.4 mg/L after being diluted 10 times. Although no distinct peak was observed, the absorbance at 254 nm (UV254) was chosen due to its widespread use in organic matter assessment in water treatment.
2.2 **Correlation Between UV Absorbance and COD**:
Nine samples were analyzed, and the results showed a strong linear relationship between UV254 absorbance and COD. The regression equation was:
**COD = 317.87 × UV254 - 67.99**, with a correlation coefficient **r = 0.9984**.
Additionally, the difference between UV254 and UV365 (ΔUV) was studied. The regression equation for ΔUV was:
**COD = 3158.25 × ΔUV - 280.21**, with **r = 0.9962**. Both models showed strong statistical significance.
**3. Conclusions**
- The linear range for COD determination using UV254 and ΔUV is 0–250 mg/L, with correlation coefficients above 0.995.
- No pretreatment of the sample is required, simplifying the process.
- UV254 is more practical and accurate than ΔUV for evaluating COD in landfill leachate, due to its higher correlation and ease of measurement.
This study demonstrates that UV spectrophotometry is a viable and efficient technique for monitoring COD in landfill leachate, offering a promising alternative to traditional methods.
**Keywords**: UV spectrophotometry; landfill leachate; UV-1200; COD determination.
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