Part 3: Process and Design Rationale for Source Separation in Industrial WWTPsBy: Dr. Hossein Ataei Far1. IntroductionOnce source separation is ...
Published on by Hossein Ataei Far, Ambassador for Sustainability | Water & Energy PPP Finance Facilitator
By: Dr. Hossein Ataei Far
1. Introduction
Once source separation is recognized as a fundamental design principle, the key question is no longer whether separation is required, but which wastewater streams must be segregated and for what technical reasons.
Industrial facilities typically generate multiple wastewater streams with distinct origins, compositions, and discharge patterns. Treating these streams as a single influent ignores basic process incompatibilities and exposes downstream treatment systems to avoidable operational risk. Both recent research and full-scale operating experience clearly demonstrate that effective industrial wastewater treatment depends on classifying streams based on process compatibility, not on convenience of collection.
2. Basis for Wastewater Stream Classification
Wastewater stream classification must be guided by parameters that directly affect treatment kinetics, biological stability, and process selection. The most critical parameters include:
✅Organic strength (COD/BOD)
✅Biodegradability and treatability
✅Presence of inhibitory or toxic compounds
✅ pH range and buffering capacity
✅Hydraulic variability and discharge mode (continuous vs. batch)
✅Oil, grease, and emulsion content
✅Metal and inorganic contaminant concentrations
Evidence across multiple industrial sectors shows that streams differing by one order of magnitude or more in any of these parameters exhibit fundamentally different treatment behaviors and should not be co-treated without appropriate safeguards (Zhang et al., 2021).
3. High-Strength Organic Wastewater
Characteristics:
High-strength industrial wastewater typically contains COD concentrations above 5,000 mg/L and may exceed 50,000 mg/L. Common sources include food processing, pulp and paper, chemical manufacturing, and fermentation-based industries.
Treatment Implications:
✅When treated separately, these streams are well suited for anaerobic processes, enabling high organic removal and energy recovery.
✅When mixed with low-strength wastewater, however:
▪ Anaerobic treatment becomes ineffective due to dilution
▪ Aerobic systems become oversized and energy-intensive
▪ Oxygen transfer efficiency is significantly reduced
Full-scale studies confirm that segregated high-strength streams treated anaerobically achieve higher COD removal, improved methane yields, and lower overall energy demand (Zhao et al., 2021).
Mandatory Separation Rationale:
High-strength wastewater should never be hydraulically diluted before treatment. Separation allows:
✅ Load-based reactor sizing
✅ Stable organic loading rates
✅ Protection of downstream aerobic polishing units
4. Batch and CIP Wastewater Streams
Characteristics
Batch and Clean-in-Place (CIP) streams are typically characterized by:
✅ Extreme pH fluctuations (often below 3 or above 11)
✅ High concentrations of surfactants and cleaning chemicals
✅ Intermittent and unpredictable discharge patterns
Treatment Implications:
Even with equalization, these streams can severely inhibit nitrification and methanogenesis. Short-duration CIP discharges have been shown to suppress microbial activity for extended periods, resulting in lasting loss of treatment capacity (Wei et al., 2022).
Mandatory Separation Rationale
Batch and CIP streams should be:
▪ Collected in dedicated holding tanks
▪ Neutralized and conditioned before blending
▪ Treated independently when toxicity exceeds biological tolerance limits
5. Oily and Emulsified Wastewater
Characteristics:
Oily wastewater contains free, dispersed, or emulsified hydrocarbons and commonly originates from petrochemical, metal processing, and food industries.
Treatment Implications:
✅Oil and grease impair biological treatment by:
✅Reducing oxygen transfer efficiency
✅Hindering microbial attachment in biofilm systems
✅Promoting foaming and sludge flotation
Emulsified oils are particularly harmful if not removed prior to biological treatment (Chen et al., 2020).
Mandatory Separation Rationale:
Oily streams require dedicated pretreatment, such as oil–water separation or dissolved air flotation (DAF), before entering biological processes. Mixing these streams with general influent increases fouling, instability, and maintenance demands.
6. Metal-Bearing Wastewater
Characteristics:
Metal-bearing wastewater is generated by surface treatment, electronics manufacturing, mining, and chemical industries. Metals such as copper, zinc, nickel, and chromium are toxic even at low concentrations.
Treatment Implications
Unlike organic inhibitors, metals accumulate in biomass and sludge, leading to:
✅Gradual loss of biological activity
✅Poor sludge settleability
✅Long-term deterioration of process performance
These effects are often delayed, making diagnosis difficult once metals enter the main treatment train (Liu et al., 2023).
✅Mandatory Separation Rationale
Metal-bearing streams must be:
▪Collected separately
▪Treated using physico-chemical methods (e.g., precipitation)
▪Discharged to biological systems only after confirmed metal removal
7. Low-Strength Utility and Cooling Water
Characteristics:
Utility and cooling water streams are typically high in flow but low in pollutant concentration.
Treatment Implications
When mixed with higher-strength wastewater, these streams:
✅Increase hydraulic loading without improving treatment performance
✅Inflate reactor volume and aeration demand
✅Reduce overall process efficiency
Unnecessary hydraulic dilution is recognized as a major cause of energy inefficiency in industrial WWTPs (IWA, 2021).
✅Mandatory Separation Rationale
Low-strength streams should be:
▪ Treated separately for reuse
▪ Bypassed where regulations allow
▪ Introduced only after treatment of higher-risk streams
8. Design Rule and Risk-Based Framework
Based on consolidated research and operational evidence, the following design rule is broadly validated:
Wastewater streams that differ by one order of magnitude or more in COD, toxicity, or pH should not share primary treatment units.
This rule provides a practical, risk-based framework for stream segregation in both new designs and retrofit projects.
9. Alignment with Water Environment Federation (WEF) Best Practices
The principles outlined above are strongly aligned with the long-standing design and operational guidance of the Water Environment Federation (WEF), which is based on decades of full-scale industrial wastewater treatment experience across North America and globally (WEF, 2016; WEF, 2018).
WEF technical manuals, industrial wastewater guidance documents, and case studies presented at WEFTEC consistently identify influent variability and incompatible stream mixing as leading causes of biological process instability in industrial and high-strength municipal treatment systems (WEF, 2016; WEF, 2018).
Key WEF best practices relevant to source separation include:
Load-based design over flow-based design: WEF guidance emphasizes that biological reactor sizing should be governed by organic and toxic load, rather than average flow. Source separation enables accurate load characterization and prevents hydraulic dilution of critical wastewater streams (WEF, 2018).
Mandatory segregation of inhibitory streams: WEF case studies repeatedly demonstrate that streams containing extreme pH, surfactants, solvents, oils, or metals must be isolated and pretreated prior to biological treatment to avoid chronic or shock toxicity (WEF, 2016).
Protection of biological processes as a primary asset: WEF frames biological treatment units as long-term assets whose performance and lifespan depend on influent stability. Segregation of high-risk streams is therefore considered a core operational risk-control strategy (WEF, 2018).
Energy and lifecycle cost optimization: In line with WEF sustainability guidance, eliminating unnecessary hydraulic dilution through stream separation reduces aeration demand, reactor volume, and overall lifecycle energy consumption (WEF, 2020).
Operational data compiled and presented by WEF show that facilities implementing structured stream segregation consistently achieve higher process uptime, faster recovery from operational upsets, reduced sludge variability, and lower chemical and energy consumption (WEF, 2016; WEF, 2020).
These outcomes reinforce that source separation is not an optional optimization, but a foundational element of resilient, energy-efficient, and sustainable industrial WWTP design.
10. Conclusion
Wastewater stream classification is not an academic exercise—it is a core risk management tool embedded in engineering design. Failure to segregate incompatible streams leads to oversized systems, unstable operation, and elevated lifecycle costs.
In contrast, systematic separation of high-risk streams enables:
✅ Appropriate process selection
✅ Improved biological stability
✅ Lower energy consumption
✅ Greater operational and regulatory resilience
The next section will quantify the operational and economic benefits of source separation using full-scale performance data and lifecycle cost analysis.
This picture was taken from the website of Conversion Technology Inc.
References:
[1] Chen, Y., Li, X., Wang, D., & Zhao, Y. (2020). Impact of oil and surfactants on aerobic and anaerobic wastewater treatment systems. Bioresource Technology, 314, 123725.
[2] International Water Association (IWA). (2021). Energy efficiency in wastewater treatment: Best practices and emerging approaches. IWA Publishing, London, UK.
[3] Liu, H., Zhang, Q., Chen, J., & Wang, Y. (2023). Long-term impacts of heavy metals on biological wastewater treatment stability and sludge characteristics. Journal of Cleaner Production, 382, 135261.
[4] Wei, W., Sun, P., Li, J., & Huang, X. (2022). Limitations of equalization for toxicity control in industrial wastewater treatment systems. Water Research, 215, 118252.
[5] Zhang, L., Zhou, Y., Liu, Y., & Chen, Z. (2021). Source separation and load-based design for industrial wastewater treatment plants. Journal of Environmental Management, 289, 112492.
[6] Zhao, X., Wang, S., Li, Y., & Chen, H. (2021). Energy-efficient treatment of high-strength industrial wastewater through stream segregation and anaerobic processes. Bioresource Technology, 331, 124984.
[7] Water Environment Federation (WEF). (2016). Industrial Wastewater Management, Treatment, and Disposal (Manual of Practice No. 8, 3rd ed.). WEF Press, Alexandria, VA.
[8] Water Environment Federation (WEF). (2018). Design of Biological Wastewater Treatment Systems (Manual of Practice No. 8 & ASCE Manual No. 76). WEF Press, Alexandria, VA.
[9] Water Environment Federation (WEF). (2020). Energy Conservation in Water and Wastewater Facilities (Manual of Practice No. 32). WEF Press, Alexandria, VA.