Monitoring Nitrates in Drinking Water and Wastewater
Monitoring Aromatic Organics for Optimizing Coagulation
Disinfection By-Products (DBP) Precursor Monitoring
Water Distribution System Security Monitoring
Importance of Measuring UV Transmittance (UVT) for UV Disinfection
Benefits of UV Transmittance (UVT) Field Testing for Selling & Servicing UV Disinfection Systems
Monitoring Aromatic Organics for Optimizing Coagulation
With the increasing awareness about the negative effects of organics within the water and wastewater treatment process along with increasingly strict water quality regulations, the need for more effective organics removal is becoming more important.
One of the most problematic types of organics is the aromatics. The ring structure of carbon atoms in aromatic molecules causes them to readily attach with various functional groups. This makes highly aromatic organics generally more reactive than other organics. Examples of aromatic organics are humic acids, such as tannins commonly found in surface water sources. Non-aromatic (aliphatic) organics include fulvic acids and other types of less reactive organic molecules.
Due to the reactive nature of aromatic organics, they more readily combine with disinfectants such as chlorine, creating disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). Aromatic organics will also combine more easily with chemicals used for coagulation, consuming the coagulant and negatively impacting the process, affecting their treatment performance. Therefore, monitoring of aromatic organics is an important aspect of any water or wastewater treatment plant operation.
UV Detection of Aromatic Organics
Organic matter, especially aromatic type organic matter, readily absorbs UV light because of the strong absorption properties of the double bonded carbon atoms present in aromatic organics. Because natural organic matter (NOM) generally contains fairly high aromatic content, measuring the amount UV light absorbed or transmitted through the water indicates the amount of natural organic matter (NOM) in the water.
Role of SUVA
Another water quality parameter that is becoming increasingly referenced especially for coagulation applications but also for chlorination applications is Specific UV Absorbance (SUVA). SUVA is simply the measurement of UV absorbance at the 254nm wavelength (UV254) divided by the measurement of dissolved organic carbon (DOC). This allows the aromatic biased UV254 measurement to be normalized over the overall organic load in the water. A characterization of the aromaticity of the water independent from the general level of organics in the water can then be obtained.
In general, it is accepted that if the SUVA of the raw water is greater than 2, then UV254 will be the best way to determine coagulation dosing. If the SUVA is less than 2, then the turbidity of the water will likely play a role in coagulation dosing since the level of aromatic organics is relatively low. It should be noted that, in general, most surface waters contain significant amounts of aromatic organics and therefore have SUVA values of greater than 2, making UV254 the parameter of choice for most coagulation dosing applications.
UV254 or UV Spectrum Analysis for Coagulation
UV254 is generally accepted as an excellent water quality parameter for coagulation optimization. However, measuring the UV spectral absorbance of the water can provide additional information that often can improve the potential optimization. This is especially true when the matrix of organics changes significantly over time.
In addition, spectrum analysis enables compensation for the effects of turbidity on UV absorbance. In many cases the turbidity is low enough that it has little effect on the UV absorbance and so monitoring of UV254 will suffice. However, when monitoring UV254 for applications where turbidity levels climb upwards of 10 NTU, a five micron filter will often be recommended to remove the excess turbidity. With spectral analysis the use of a filter is not necessary for physical removal of turbidity since its effects on the UV absorbance data can be mathematically removed.
Real Tech's products for coagulation control include the Real UV254 'M' series for continuous real time monitoring of the UV254 parameter, and the Real Spectrum series of continuous analyzers for UV spectral analysis with turbidity compensation. The Real UV254 'P' series portable meters are also useful for grab samples and for initial coagulation dose determination via jar testing in the lab.
Coagulation Process Control
Real Time UV Absorbance Monitoring Ensures Coagulation Optimization
For proper coagulation optimization, monitoring of UV254 or UV spectrum analysis should be performed both before and after the coagulation process. Real Tech offers its Dual Feed option for both the Real UV254 'M' series and the Real Spectrum series instruments. The Dual Feed feature enables one instrument to be used for two sample water feeds which in this case would be the raw and treated water. The two measurements can be compared to provide percent removal of organics by the coagulation treatment process. The plant's goals for effectiveness of the coagulation process, whether it be 40% or 60% removal of organics, can be continuously monitored, providing a real time understanding of the effectiveness of the coagulation process.