Chemical costs are often the most significant operating expense for industrial wastewater treatment systems, far surpassing energy costs. For example, running a PCL-60 DAF system at full capacity (660 gallons per minute) for 24 hours costs roughly $30 in electricity. However, chemical costs, determined by flow rate and wastewater composition, can amount to five or six times that figure annually.
Reducing chemical usage is not just a cost-saving opportunity but also a step toward more efficient and sustainable operations. Here are seven actionable strategies to optimize chemical consumption in your DAF system:
1. Equalize and Mix Flow
Achieve consistent wastewater quality by collecting and homogenizing all plant wastewater, including rainwater and yard runoff. Mixing high-solids streams with lighter loads dilutes the solids concentration, allowing for flow-paced chemical dosing rather than reacting to peaks and valleys. This proactive approach minimizes the need for additional chemicals to handle variations in loading.
2. Use Pre-Screening Equipment
Reducing the volume of solids entering the DAF system is crucial. Simple mechanical screens, such as rotary drum screens or tight floor drain screens, can significantly lower total suspended solids (TSS). By removing easily separable solids mechanically, chemical dosing can focus on harder-to-separate contaminants, improving efficiency and reducing costs.
3. Calibrate Dosing Pumps
Accurate dosing is essential to avoid waste. Calibrate your liquid chemical feed pumps regularly using a graduated cylinder to measure output at various settings (e.g., 10% to 90% capacity). For example, if your pump delivers 35 ml/min instead of the intended 30 ml/min, you’re overdosing by 15%. Proper calibration can save thousands of dollars in unnecessary chemical expenses.
4. Use the Right Chemicals for pH Adjustment
Using coagulants to adjust pH is inefficient and costly. Instead, rely on dedicated pH reagents, such as sulfuric or hydrochloric acid, to bring wastewater to a neutral range. Metal-based coagulants like aluminum or iron should only be used for their intended purpose—coagulation within the appropriate pH range—not for pH adjustment. This approach improves both cost efficiency and overall treatment performance.
5. Optimize Chemical Dispersion
Proper chemical dispersion ensures maximum effectiveness. In DAF systems, chemicals are introduced via mixing tanks or pipe flocculators. Mixing tanks use mechanical agitators, while pipe flocculators rely on flow velocity and shear forces. Both methods can work effectively, but adherence to operational guidelines is critical. Regularly evaluate your dispersion method to ensure chemicals are being used efficiently.
6. Treat to Permit Requirements
Over-treating wastewater can be unnecessarily expensive. If your permit requires TSS levels below 250 mg/L, aim to meet but not significantly exceed that limit. While clear water with <10 mg/L TSS might look impressive, it’s not always necessary. Use only the minimum amount of chemicals required to remain compliant with regulatory limits, balancing cost and performance.
7. Conduct Regular Jar Tests
Jar testing is one of the simplest ways to optimize chemical dosing. Collect a wastewater sample, add incremental doses of coagulant using a pipette, and observe coagulation. This quick test allows for real-time adjustments to dosing rates, ensuring you use only what’s needed. Regular jar tests can prevent chemical overuse and maintain effluent quality within compliance limits.
A Word of Caution
While reducing chemical usage is a worthy goal, eliminating chemicals entirely can lead to inefficiencies and higher costs elsewhere. For example:
Poor Sludge Quality: Without coagulants or flocculants, many suspended solids remain in the water, leading to watery sludge and suboptimal effluent quality. This shifts costs from chemical treatment to sludge management and biological processes.
Lost Value in Recovered Solids: In some industries, such as rendering, adding chemicals enhances solids recovery. The additional recovered product often offsets the cost of the chemicals, improving profitability.
Each situation requires careful evaluation to balance cost savings with operational effectiveness.
Conclusion
Optimizing chemical use in your DAF system can lead to significant cost savings without compromising performance. By implementing strategies like equalizing flow, pre-screening, calibrating dosing pumps, and regularly testing dosing rates, you can ensure efficient operation while maintaining compliance with regulatory requirements.
For more guidance on improving your DAF system’s performance, reach out to our experts at FRCInfo@sulzer.com.
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