Every project is unique, with its own set of operational, waste management, and end-user goals. Assuming that projects are identical can lead to ineffective wastewater treatment solutions.

Pitfalls to steer clear of and best practices to follow to avoid costly missteps and regulatory headaches

In the realm of waste management and biogas production through anaerobic digestion, understanding the unique characteristics and requirements of each project is crucial. Missteps can lead to inefficiencies, higher costs, and compliance issues. Here we explore common pitfalls and provide practical suggestions to guide successful project execution.

Common Pitfalls in Project Evaluation

• Assuming Project Similarities: Every project is unique, with its own set of operational, waste management, and end-user goals. Assuming projects are identical can lead to ineffective solutions and unmet objectives.
• Organic-Only Focus: Focusing solely on organic aspects can neglect essential nutrients and ionic activity, affecting overall performance and effluent characteristics.
• “No Feed” Periods: Bacterial activity during periods of no production, such as nights or weekends, can be uncertain and might disrupt processes.
• Incomplete Characterization: Failing to fully understand operational conditions can result in improperly sized equipment and affect the quality of the digestate.
• Not Defining Regulatory Requirements: Lack of awareness of local regulations can compromise the effectiveness of secondary and tertiary treatments.
• Not Defining Treatment Needs: Unclear plans for digestate treatment, effluent discharge, and biogas use can hamper project outcomes.
• Incomplete Mass Balance: Neglecting a complete mass balance can lead to uncontrolled reactions, precipitation, and process problems.
• Focus on CAPEX vs. OPEX: Focusing solely on capital expenditures without considering operational expenses and return on investment can be detrimental.
• Using Biogas: Not having clear goals for biogas use, whether to meet regulations or generate income, can lead to project inefficiencies.

Common Pitfalls in Anaerobic Digester Design

• Overly Focused on HRT and OLR: While solids retention time (SRT) is crucial, an excessive focus on hydraulic retention time (HRT) and organic loading rate can overlook other critical factors in anaerobic digester design.
• Failure to Predict Precipitation: Ionic activity, metals, and salts can cause uncontrolled precipitation, leading to scaling, equipment failure, or reduced operational volumes.
• Overly Broad Biomethane Production (BMP) Assumptions: Assuming constant BMP can be misleading, as gas composition and yield can vary significantly.
• Assuming Low-Rate Is Safer: Overly conservative low-rate systems can create operational challenges and require more space than is necessary for treatment.
• Minimizing the Importance of Digestate: Without proper inlet characterization, predicting digestate quality is difficult, affecting wastewater treatment plant functions and increasing chemical operational expenses.
• Incomplete Picture of Sulfur: Overlooking sulfur’s impact can affect biogas quality and lead to solids formation in the reactor.
• Ignoring Chemical Balances: Failing to balance chemicals can hinder bacterial growth, causing souring or foaming.
• Overly Large Tankage: Larger tanks can be challenging to mix and maintain pH, leading to premature solids settling or excessive operating costs.
• Control and Automation Flexibility: Traditional systems may lack the control measures necessary to predict and prevent process upsets.
• Design of Ancillary Systems: Ancillary systems like digestate treatment, dewatering, biogas upgrading, recirculation, heat exchangers, and flares need detailed review and consideration.

Common Pitfalls in Acclimation and Operation

• Acidification and volatile fatty acid (VFA) Formation: Overfeeding leads to excess VFA formation, pH drop, and foaming, disrupting methanogenic bacteria activity.
• Alkalinity and Nutrient Control: Improper alkalinity and chemical control result in solids settling, salt toxicity, and foaming; correct nutrient additives are crucial.
• Uncontrolled Precipitation: Ignoring ionic activity causes scaling and formation of compounds like calcium phosphate and struvite.
• Seeding and Ramp-Up: Overseeding or rapid start-up with high organic loads leads to excessive VFA formation and operational instability.
• Temperature Control: Stabilizing inlet and recycle temperatures improves performance and reduces energy requirements.
• Lab and Monitoring: Lack of real-time monitoring creates operational challenges.
• Feedstock Consistency: Inconsistent waste characteristics affect nutrient and chemical operations.
• Digestate Treatment Costs: Treating digestate incurs high operational expenses from managing inorganic and ionic activities.
• Toxicity or Shock: Mixed waste or varying feed conditions can lead to toxicity from high concentrations of Nh5, NH3, sulfide, nickel, and iron.

Best Practices: Don’ts

• Oversimplify Design Conditions: This can lead to inadequate solutions.
• Assume All Projects Are the Same: Each project is unique and requires tailored approaches.
• Focus Only on Organic Loading: Consider the full spectrum of nutrients and ionic activities.
• Forget About Ionic Activity: It plays a crucial role in the process.
• Overlook Potential for Precipitation: Be aware of and manage precipitation risks.
• Assume Bigger Is Better: Design appropriately for each circumstance and end goals.
• Assume Biomethane Yields: Validate assumptions with real data.
• Forget About Sulfur: Sulfur can significantly impact biogas quality.
• Forget About Control Flexibility: Ensure systems can manage variances.
• Minimize Importance of Ancillary Treatment: These treatments are vital and should not be overlooked.
• Rush Acclimation Period: Allow adequate time for bacterial acclimation.

Best Practices: Dos

• Understand Feeds and Mass Balance: Thoroughly understand feed inputs and develop a detailed mass balance, using it to predict precipitation, scaling, and micronutrient requirements.
• Identify Differences in Infrastructure, Logistics, and Regulatory Drivers: Recognize and account for these differences early on.
• Understand All Nutrient, Metals, Salts, and Mineral Inputs: Comprehensively understand all inputs to the system.
• Understand Air, Land, and Water Discharge Requirements: Know and plan for local regulations.
• Evaluate Site OPEX: Assess operational expenses, including hauling, electrical use, logistics, and byproducts.
• Understand SRT Requirements: Determine the specific SRT needs for the waste type.
• Review Potential for Struvite and Scaling: Evaluate possible issues with struvite, calcium phosphate, and scaling.
• Evaluate System Designs for Performance: Consider mid- and high-rate systems, and multiple process tanks for better performance.
• Develop Waste Profiles: Accurately profile waste and chemical oxygen demand (COD) reduction efficiency.
• Calculate hydrogen sulfide (H2S) Potential: Assess H2S potential in biogas and necessary treatments.
• Consider Biomass and Effluent Recirculation: Stabilize biota and temperature through recirculation.
• Use Sensors and Dosing Systems: Implement sensors and dosing systems for better management.
• Design for Digestate Quality: Ensure that the anaerobic digester system accounts for digestate quality and necessary treatments.
• Incorporate Efficiency: Include biogas cleaning, chemical skids, dewatering, and solids treatment in the design.
• Feed Resources and Chemicals: Prepare adequate feed resources and chemical adjustments.
• Seed with Similar Sludge and Gradually Increase Feedstock: Start with similar sludge and ramp up feedstock over time.

By avoiding common pitfalls and following best practices, you can enhance the efficiency, compliance, and overall success of your waste management projects. Let Fluence be your partner in achieving optimal waste management results. Contact us to start building a successful, sustainable solution for your operations.