Sustainable Design for High Strength Wastewaters
Sustainability – Climate Change
Pro-action, although late, is urgent to implement climate change policies authenticated by the Paris Agreement (2015) to achieve UN Sustainability Development Goals (SDG).
Lead objectives are to comply with ongoing global policies on:
• Carbon Footprint (CF) reduction/ultimate carbon neutrality
• Minimisation of Greenhouse Gasses (GHG) production
• Minimise production of ‘Excess solids and liquids’ which offset ergonomic mass balances of nature
• Where possible utilise biology/biochemistry to apply the principles of the overlapping C, N, P and Water cycles
• Minimise imported energy
• Maximise green energy, including bioenergy
Industrial management and practice require ongoing strategy decisions, concept to conclusion, relating to any combinations of:
• Raw solids
• Waste solids
• Outsourced energy; electric or gas
Earlier masterplans were less curtailed in relation to sustainability-related ethics. Emerging initiatives require overriding sustainability to address all the above issues in combination.
Fundamental restrictions relate to carbon, nutrients, by-products (not convertible to co-products) and advanced stage toxin carryovers (pesticides, herbicides, microplastics, etc.) must now be addressed at concept stages.
Most of engineering guide-value norms require an annual audit to ensure fundamentals such as GHG rating, CF rating, risk-averse minimum energy policies, temperature extremes, hydraulic trends/critical peaks, non-sustainable by-products etc are classed as Hazop issues.
Objectives of engineering and management must now aim to apply more biosphere – friendly technologies, make decisions after proper carbon/nutrient audits, conduct R&D into concepts destined to minimise imported energy/CF and convert renewables digestate solids, incinerator ash and retentate TDS into reusable co-products.
This is a major challenge to all engineers, R&D practitioners and industrial leaders with practical responsibility. Proactive new research is vital and field development of this research must follow in a positive in the subsequent short term.
Commercial sustainability allows the cost-conscious application of the above fundamentals. Mutual considerations of rate-of-return and sustainability index may give the optimum answer. CF, water footprint (WF), environmental mass balance, and co-product technology will define engineering ethics in the future.
This is categorised here:
• Carbon, Nitrogen, Phosphorus, Water Cycles
• Wastes: Solid & Liquid: Recycle/Capture
• Energy potential of renewable feedstocks
• Excess sludges (biological/chemical)
• Soil nutrients, biocide and pesticide level
• Advanced Wastewater Treatment – Re-Use
High Strength Organic Wastewaters
High-strength wastewaters which is herein defined as organic in nature, requiring carbon and nutrient removal to a designated level of quality. The wastewaters result from raw product/final product/co-product carryover in washwater from production systems. Prime sources are food processing, brewing and distilling, soft drinks, agricultural slurries and run-offs, digestion sideflows, landfill leachates pharma-biopharma wastewaters may now be included in this category.
Points of relevance in assessing high-strength wastewaters:
• Concentrations in a volume may relate to organic carbon, nutrients or both.
• The process evaluation should be biased by relative biodegradability, biochemistry and, where relevant, by Biochemical Methane Potential (BMP).
• Typical high-strength wastewaters may vary from 1,000mg/l COD up to 100,000mg/l COD and the nutrient ratios and treatability require inclusion.
• Readily biodegradable COD as an indicator of reaction rate and enzyme/co-enzyme activity.
• Trend curves relating to inhouse production to emission over the periods and phases of production are an advantage.
• Proper pre-conditioning is necessary for all relative assessments.
• Sustainability analysis may be carried on existing plants after a detailed site/process survey including an energy audit.
• Alternative designs should be considered using comparative carbonation (CF Diligence) analysis to identify the optimum solution.
In all cases a confident evaluation of outfall characteristics is essential. This may justify studies which, ideally, should relate to in-house production.
Phased development and versatility of treatment capacity is a required input and a contingency is often desirable for possible change of product specification.
Typical values of high strength wastewaters are noted for reference in Table 1
Note: Values variable within-house production, scale and solids loading
Conventional v Sustainable
All designs should now aim to apply sustainability design ethics.
• Confirm committed design loading trends and performance
• Record the intimate as-constructed works detail, results and operational issues on existing plants and energy audit detail on existing plants
• Gather cost information sources, Capex and Opex
Each application requires a review of viable alternatives to achieve and, on this basis, a framework of projects may be listed for comparative assessment.
To upgrade conventional process/plant technology the basic design is reviewed from energy/modulation, sludge production, stability under varying loading, level of automation, mechanism(s) to minimise ongoing chemical and demand and ease of process control.
Modifications to minimise energy, sludge generation, and chemical usage are leaders in sustainable design. Concepts such as
• Use of biology as an adjunct to biochemistry
• Minimising oxygen demand (SOR) via sequencing and automation.
• Process modification to utilise low DO bacterial performance
• Use of anaerobic digestion for carbon reduction, ideally with resulting bioenergy
• Further prevalence of bacterial cohabitation in sequencing reactors
• Adapt systems for low energy nitrogen removal with minimum carbon requirement
All modifications result in a related cost which requires comparison prior to rating the alternatives. This rating covers the above fundamentals and is tainted at all times by CF reduction guidelines.
Commercial Viability of Sustainable Alternatives
Biologically treatable High strength wastewaters are likely to become more dominant as water use is reduced in production and out of process waters (e.g. cooling, condensates etc.) are recycled at source. This will prioritise minimum-energy mainstream pre-treatment with bio-energy recovery for reuse.
Ideally the concept should maximise organic carbon pre-treatment/removal by anaerobic digestion of the main effluent load (‘mainstream’) but ensure that the secondary and tertiary stages of treatment will accommodate required nutrient removal.
The following points relate:
• Sludges are reduced to <10% of that from the equivalent aerobic process (EAS) while the reusable nutrients remain in a more concentrated form.
• Aeration energy costs can be reduced from 100% using conventional systems down to 15% – 20% using mainstream pre-treatment.
• The above figures may vary if pre-treatment pre digestion is found necessary. Sustainable reuse of sludges, e.g. fats/oils/greases, so produced may reduce costs earlier incurred.
• Judicious design of downstream polishing to produce desired quality is required.
• On-line control without over-complication from local loops will ensure modulation. This will accommodate the ideal namely to ‘provide biotreatment at irreducible minimum cost’
• An overriding criterion for conclusive consideration is additional cost implications at capex stage versus ongoing potential savings with allowance for implications of BAT and Climate change regulations.
Typical Case Studies’ Cited
Most treatment systems of earlier design did not properly address the conservation of energy or the effect of carbon and allied nutrients on CF.
Sustainability audits will determine the extent and scale of the upgrade desirable and the viable reuse of outdated machinery on the existing site.
Design criteria, operating data, and valuable O&M log reports-site feedback aid the assessment which, in turn, allows updated modifications to process and machinery so that the plant becomes state-of-the art.
For new plants, at masterplanning stages, detailed design requires analytical confirmation of BMP and research on the performance of AD pre-treatment knowing the confirmed equalised feedstock analysis trends.
Installations of this technology confirms that the concept is a proven leader in sustainability technology. The downstream treatment requirement to produce final outfall quality to standard requires case by case judicious selection. Comparative total cost analysis of state-of-the-art versus a conventional all-aerobic system show the major advantages while offering the most sustainable solution in terms of GHG/Climate change.
Typical examples are as follows:
1. Reference Project 1 – Ireland – Dairy Industry
2. Reference Project 2 – Ireland – Distilling
3. Reference Project 3 – Ireland – Fishing Processes
• Practitioners must aspire to emerging fundamentals whereby sustainable practise minimises climate change
• Process design and material selection should aim to reduce carbon footprint (CF) and minimise GHG emission.
• Wastewater designs must show more eco-friendly processes with less reliance on oxygen, external energy and chemicals
• Creation of high strength organic wastewaters with good treatability allows application of anaerobic technology on mainstream flows – so minimising CF and GHG emissions.
• Typical industrial sectors to benefit from this are dairy, meat, distilling, brewing and the wider range of organics, biopharma and organically quantified solids.
• The post AD stages of treatment are an integral part of the sustainable answer if high quality secondary, tertiary or advanced stages of treatment are under consideration.
• The conversion of outdated processes and plants, not now utilising BAT, is a major practical challenge to management and engineering.
• As time and R&D evolves the objectives of low energy/minimum excess sludge and modulated operation is likely to utilise the more sustainable technologies on less concentrated organics.