Renewable energy, anaerobic digestion, sustainable development

CARBON EMISSION AND GLOBAL WARMING

Global warming, which means the increase of the average global temperature of the Earth’s climate system, has far-reaching negative impacts on the human population and ecosystems and is the biggest challenge to achieving sustainable development. The predicted negative effects of global warming include increased unpredictability of the weather and climate; dramatically increased severity, scale, and frequency of extreme weather events such as storms, heatwaves, droughts, and flooding; melting of ice sheets, which contributes to rising sea-levels; changes to regional climate; food and freshwater availability; and biodiversity loss.

 

Human activity is the dominant driver for the observed warming in the industrial era, and the largest anthropogenic contributor is the emission of greenhouse gas such as carbon dioxide. Carbon dioxide from the burning of fossil fuels and industry is the largest source of greenhouse gas, accounting for about three-fourths of total global emissions.

 

Many impacts of global warming have already been observed, such as declines in the Arctic sea ice extent, extreme weather events, and rising sea-levels to name a few. Some of these impacts are also already visible in Ireland: increased number of warm days and decreased number of annual frosty days, increased average annual national rainfall (60mm higher in the period 1981 to 2010 than the period 1961 to 1990), increased river-flow, increased mean annual sea surface temperature (1.0°C higher than that during 1961-1990, as measured at Malin Head, Co. Donegal), a sea-level rise of 1.7cm per decade.

 

The impacts of global warming can reach levels of irreversibility if global warming exceeds ‘tipping points’, beyond which certain impacts become irreversible even if temperatures are reduced. To avoid some of the irreversible impacts, keeping global warming below 1.5 °C compared to pre-industrial levels is needed, as emphasized by the Intergovernmental Panel on Climate Change (IPCC). We have to reduce global carbon emissions by 45% from 2010 levels, by 2030 in order to reach the carbon neutrality target by 2050. We only have a limited window to limit global warming to 1.5 °C, which would require rapid and unprecedented changes in all aspects of governments, industries, and societies.

Global Temperature July

Reference: https://twitter.com/rahmstorf/status/1162071379740639233

EU and Ireland’s effort to curb global warming: the role of renewable energy

 

The European Union has set binding targets to curb global warming by reducing greenhouse gas emissions, including reducing greenhouse gas emissions by at least 40% below 1990 levels by 2030.  Increasing the use of renewable energy, i.e., energy from renewable sources, is an important part of the package of measures needed to achieve these goals. The European Union is aiming at increasing the share of renewable energy to at least 32% of EU energy use by 2030. Each Member State is required to submit a 10-year National Energy and Climate Plan (NECP) to set out its contribution to these targets and how to reach these targets.

 

According to Ireland’s draft NECP, Ireland can expect renewable energy share of 15.8 – 19.2% by 2030 (without additional measures) and 23.7 – 27.7% with additional measures, which are less than the required target of 31% (results from Regulation (EU) 2018/1999 on the Governance of the Energy Union and Climate Action). The final NECP will be a binding plan and missing the target may lead to fines. On the other hand, Ireland is on track to miss its 2020 renewable energy targets of 16% and ranked 26th out of 28 member states in EU (as of 2019) in terms of its progress towards renewable energy targets. Transformative changes in industries and societies in terms of energy utilization are needed to achieve Ireland’s goals.

 

Renewable energy from anaerobic digestion

 

Anaerobic Digestion is a process where several groups of microorganisms breakdown organic non-woody components in the feedstock in the absence of oxygen. Anaerobic digestion produces biogas and digestate. Digestate contains nitrogen and phosphorus and can be used as fertilizer. Biogas mainly consists of methane, the same chemical compound contained in natural gas and can be used directly as fuel for combined heat and power engines or upgraded and injected into the natural gas network. Common feedstocks for anaerobic digestion include wastes such as slurry and manure from cattle, poultry, and pigs, domestic food waste, organic wastes and wastewaters from food and beverage processing industries, and grass and maize, etc 

 

Anaerobic digestion is a source of renewable energy and can reduce carbon emissions by generating bioenergy from carbon. This can replace fossil fuel with renewable biomethane. Biomethane is a product certified by Gas Networks Ireland with standards equivalent to natural gas for grid injection.  

In addition to the provision of renewable energy, anaerobic digestion also facilitates reduced carbon footprint, greenhouse gas reduction, sustainable waste treatment, nutrient recycling, soil carbon sequestration and CO2 separation for reuse in industry, at a dedicated RenewablCentres. 

There is no shortage of potential indigenous anaerobic digestion feedstock in Ireland: roughly 7 million cattle, 5.2 million sheep, 1.5 million pigs, and 11 million poultry, together with waste arising from crop farming industry and households (as of 2016)It is predicted that carbon emission savings of up to 0.7 Mt CO2e/year by 2030 and 2 Mt CO2e/year by 2050 can be achieved using anaerobic digestion to produce biogas. 

To achieve the aforementioned carbon emission savings, methane production of around 300 million m3 by 2030 and 1200 million m3 by 2050 is required. Assuming each anaerobic digestion plant produces methane at a rate of 11.4 Nm3/hr (0.1 M m3/year)this would require the establishment of around 300 anaerobic digestion plants by 2030 and 1200 by 2050, which could be an achievable goal if we look at the development of anaerobic digestion in other areas of Europe.  

 

More than 17,400 biogas plants are producing 18,400 million m3 biogas (662 PJ) in Europe (as of 2015), making EU the world leader in biogas electricity production. In the EU, Germany has the highest biogas production of 9,200 million m3  with around 8,000 installations. Biogas productions in other countries are approximately 2,600 million m3 in the UK (500 plants)2,200 million m3 in Italy (1000 plants), and 260 million m3 in Belgium and Poland. Northern Ireland has also seen significant developments in the anaerobic digestion sector: 24 new installations have been commissioned since 2015 and 103 more approved or under construction as of 2017. However, anaerobic digestion in Ireland is under-developed with less than 10 anaerobic digestion plants operating in Ireland, producing 64 million m3 methane (2.3 PJ, 1.5% of natural gas consumption) as of 2015. There is great potential for the development of anaerobic digestion in Ireland, which would require encouraging policies from the government and commitments from the industry. 

AD Plants in Europe & Biogas Energy Production Graphs

Reference: Scarlat, N., Dallemand, J.-F., Fahl, F., 2018. Biogas: Developments and perspectives in Europe. Renewable Energy. 129, 457-472

WEW Engineering’s commitments

WEW Engineering is currently conducting an innovative research and development project aimed at the provision of automatic monitoring and control systems, to optimize the performance and commercial management of integrated unit operations at Renewable Centres. Further research areas include the investigation of the feedstock marketrelevant regulations, and additional aspects relating to anaerobic digestion.  

WEW Engineering is committed to optimise bioenergy recovery and to apply sustainable engineering technology in the interest of climate change, following the recommendations of the Paris agreement. 

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Distilling | Water and Wastewater

DISTILLING | WATER AND WASTEWATER

Background

The first written record of Irish whiskey dates back to 1405, making it one of Europe’s earliest distilled beverages. In 1608 the first licence to produce whiskey granted at the site that is now the Bushmills Old Distillery in County Antrim and this is where whiskey production became an industry. Since then the popularity of Irish Whiskey has grown around the world.

In 2010, four distilleries were producing around 6 million cases (72 million bottles), compared to 2019, with 31 distilleries operating on the Island of Ireland producing 10.7 million cases (130 million bottles) per annum. This phenomenal growth is expected to continue, investors and developers have pumped resources and finance into the industry in recent years. With this surge in distilleries, investment, and brands exporting their products internationally, the origin and story of the Whiskey is almost as important as the product itself.

irish-whiskey-distilleries-dec-2019-irish-whiskey-association

This has resulted in old distilleries reopening their doors and new distilleries being built in old buildings such as churches, mill houses, and stable yards for example. Many conversion projects and new builds have opted to include visitor centres to showcase their product and the beautiful settings in which they are located, which often means remote locations without access to main gas, mains water or a sewer network.

A distillery producing 1.5 million litres of pure alcohol (lpa) per annum will have a large water demand. A good option for the cooling water is to use a nearby river or lake for extraction and discharge. For example, a license may be granted to allow the discharge of 1000m3/day with a maximum temperature of 30°C separate to process effluent. During the summer when the water bodies are warmer, cooling becomes more of an issue and some borehole water may have to be used to increase cooling capacity, other options may include cooling towers or chillers. Without a connection to mains water, process water and potable water will usually be sourced from a borehole, the treatment and final quality depends on the application within the process. For example, spirit reduction and boiler feed water need to be treated using a reverse osmosis unit.

spirit reduction and boiler feed water need to be treated using a reverse osmosis unit

All the above unit operations require a large amount of electrical energy. However, the heating energy required on a distillery is greater again, and without a gas mains connection, most distilleries turn to LPG stored onsite and delivered at approximately 40c/l. Therefore, even at 100% efficiency, it would cost around €54,000 to triple distil 1.5million LPA. Good designs and specialist process selections by the Master Distiller may reduce unit energy demand (MJ/l) for the distillation process by up to 33%. Implementing energy-saving measures in a distillery offers an attractive return on investment.

 

Our Solutions

At WEW Engineering we do not believe in “one size fits all” design solutions and we tailor our designs to individual client needs and site constraints. For example, when considering using a local body of water subsidized with borehole water for cooling stills the following parameters, some of which are dynamic, need to be considered to achieve maximum energy efficiency:

• Temperature of the water body
• Max allowable discharge temperature
• Temperature of borehole water
• Hydraulic head from waterbody to the stills
• Hydraulic head from borehole to the stills
• Borehole yield

For Reverse Osmosis water borehole may not always be the best source if there is a lot of hardness or minerals in the water, this could cause excessive fouling of the RO membranes. One solution is to use rainwater harvesting, as rainwater will not have the same mineral loading. A cost-benefit analysis can be easily carried out to calculate the payback period of the extra Capex versus the savings on membrane fouling. However, solutions like this not only have a financial saving for the distillery, but they also improve the green credentials of the brand, which is very important nowadays. Reducing the litres of water used per LPA or to say the spirit is diluted with 100% Irish rain before bottling, an authentic marketing story which appeals to the target consumer. Sustainability, CO2 reduction, circular economy, water/energy/nutrient reuse, are popular marketing tools in today’s global marketplace.

Distilleries have huge opportunities to reduce their water and carbon footprints, a significant proportion of these be derived from postproduction activities. After each distillation, several by-products remain, spent grain, pot ale, spent lees and wash water. Using the example of the 1.5 million LPA per annum these products have a polluting potential equivalent to 40,000 people. The pot ale alone can have a Biological Oxygen Demand (BOD) of up to 50,000mg/l, therefore these products need to be managed correctly. Spent grain and pot ale are frequently sent for animal feed as they have a high calorific value and are high in protein. In this instance the spent lees and wash water will be considered a waste product, it may be possible to send them to sewer if one is available, but the spent lees still have a BOD of up to 2,000mg/l which is higher than most Discharge To Sewer (DTS) licences will allow. An onsite wastewater treatment plant (WWTP) will be required.

Another option which we have designed and implemented in recent years is to retain the pot ale on-site and treat it along with the spent lees and wash water in an anaerobic digester (AD). A digester treating 1,000kg of BOD per day could produce biogas with an equivalent energy value of around 1.2GWh, or €60,000 per year when compared to LPG. If a project were accepted in the Support Scheme for Renewable Heat (SSRH) the distillery would receive an extra €30,000 in grant aid per year for 15 years.

Other benefits of a well-designed AD and WWTP integration is the vast reduction in Excess Sludge (ES) production, up to 75%. Disposal of which can be one of the biggest operational costs associated with an activated sludge plant. WEW Engineering has designed systems which treat distillery effluent (pot ale, spent lees and wash water) in an AD. Downstream of this nitrogen and phosphorus are removed via Enhanced Biological Phosphorus Removal (EBPR) and concurrent Nitrification/Denitrification in an A2O process to discharge to a water body with BOD, Suspended Solids, Ammonia and Total Phosphorus licence limits of 15mg/l, 15mg/l, 3mg/l and 2mg/l respectively. This design produces a sludge high in nitrogen and phosphorus which will be spread to land to grow barley which will be used to produce more whiskey.

 

Our Services

We produce designs and reports to assist our clients to obtain planning permission, grant aid, and investor support incorporating innovations to maximise energy efficiency, nutrient and energy reuse, which guarantee environmental protection through high-quality effluents. We assess options as client representatives, our experience and non-biased approach allows us to carry out due diligence assessment of equipment, manufacture’s sales claims, and we assist our clients in making the best decisions for their project and sites.

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Wastewater

SUSTAINABLE DESIGN 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

 

Sustainability Cycle

Industrial management and practice require ongoing strategy decisions, concept to conclusion, relating to any combinations of:
• Water
• Wastewater
• Raw solids
• Waste solids
• Outsourced energy; electric or gas

 

 

sustainability

 

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.

 

Characteristics

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

Source COD TSS             COD/TKN COD/PO4
  Mg/l Mg/l
Milk 3,000 600 18 10
Meat 3,500 2,000 17.5 19
Brewing 5,500 1,000 67 110
Distilling 35,000 1,500 11 175

Note: Values variable with in-house production, scale and solids loading

 

Conventional v Sustainable

All designs should now aim to apply sustainability design ethics.
This includes:
• 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

Fundamentals

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

 

Conclusion

• Practitioners must aspire to emerging fundamentals whereby sustainable practice 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.

The impact of COVID19 lockdown on your wastewater treatment plant

Friday the 27th of March 2020 was a surreal day that we knew was coming, but that didn’t make it any easier to comprehend. The Taoiseach, Leo Varadkar  made the announcement, essentially putting the country on lockdown but for some named exceptions. “Our country is rising to this challenge, and I’m convinced we will prevail,” he said. It is inspirational to see what this country is capable of in the face of this crisis, shutting down tourism, sport, arts/cultural events and social gatherings. Not something we would have predicted, at the start of 2020! Some people are still going to work every day to keep food on the shelves, deliveries or continue production, and of course, the healthcare workers who are the real heroes fighting this war on the frontline. Our sacrifice of staying at home and working from home seems small compared to the effort the healthcare workers will continue to put in over the next few weeks.

 

Our company provides water, energy and wastewater designs and solutions, so you may ask, where does wastewater come into this? Well, it is not top of most peoples’ lists (understandably), but it is our job here at WEW Engineering to think about wastewater, which still needs to be managed. Also, water quality and emissions limits, while not the most important issue at the moment, should be upheld even in the time of a crisis. The EU holds a similar view relating to carbon reporting deadlines, upholding the April 30th deadline for firms to surrender emissions trading system (ETS). Therefore, authorities will not and should not be turning a blind eye to breaches of environmental regulations. So, the humble wastewater treatment plant (WWTP) will have to continue to efficiently and effectively discharge effluent in accordance with all EPA/Irish Water licencing and regulations.

 

Most WWTPs consist of microorganisms (biomass) which feed on the pollutants. Like most living things they thrive on a consistent and steady feeding schedule. They don’t like being starved, they don’t like being overfed and in general, they don’t like change very much. Now, in the current climate there are very few places that have avoided change so how do you look after your WWTP to make sure it will keep discharging effluent within spec and not cause any further headaches?

I will highlight a few points worth considering for any WWTP that has found itself with no wastewater to treat or with a drastically reduced loading. Having no or very little loading hardly seems like a problem, but when we all want to return to some type of new normal it would be a shame for any production line in the country to be held up due to the WWTP not working.

 

Worst-case scenario

The likely worst case is that after the WWTP being neglected for a few weeks all the biomass is dead and there is nothing in the tanks to remove pollutants. Therefore, either production is stopped, or you start to tanker wastewater away using an environmental services company. Neither of these options are economic or productive. The WWTP then must be reseeded with healthy biomass imported from another WWTP, reseeding will take 1-2 weeks depending on the process and how much biomass is imported. During reseeding the loading on the WWTP starts at 0% and increases by 5-20% per day.

However, not all the biomass will die at once; biomass which remove Phosphorus and Nitrogen are more sensitive than that which remove BOD/COD. If the population of nitrifying/denitrifying bacteria die the ammonia figures in the final effluent will be very high. Another indicator is the presence of nitrates. If no nitrates are present it means, there are no ammonia oxidising bacteria (AOBs) and you will need to import some seed biomass as a partial reseeding.

 

Best-case scenario

In an ideal world, lockdown restrictions will be lifted, and a facility would ramp back up to 100% production within a day or two and the WWTP would treat the wastewater to the required specifications as it had been doing before lockdown. The output of this production line would be hoping to go from 100% on 27/03/20 down to 0% the next day, then stay at 0% for at least 2 weeks before getting back to 100%. Production lines will be slower to get to 100% due to a wide range of issues around personal distancing in the workplace, demand forecasting and sales pipelines etc. Every site will be unique in this respect, but to look at the issue of wastewater treatment generally, let’s assume a proportional relationship between production output and loading to a WWTP. We are asking a WWTP to treat 100% load, then 0% load for at least 2 weeks and back to 100% load, this will not work.

 

Three options available to an operator of a suspended growth WWTP:

  1. Maintain WWTP at 100% loading
  2. Allow loading drop to 10-25% while keeping the biomass healthy
  3. Allow Biomass die and reseed when possible

Before we look at the options in isolation it is important to note that to give the biomass the best chance of reacting to your business needs there are a few basic items that should be addressed.

 

Dissolved oxygen

• Make sure the biomass has the right amount of air in the right places and make sure the DO instruments are reading correctly.

• Make sure the duty/standby changeover is automated on the blowers should there be an issue and the WWTP doesn’t get checked for a few days.

 

Recirculation pumps

• In certain processes, the biomass depends on cycling through different environments such as anoxic/aerated.

• If the WWTP is fitted with recirculation pumps the auto duty changeover should also be checked.

 

F:M ratio

This will be mentioned multiple times below but just to be clear and keep it simple, the food to mass (f:m) ratio is the ratio of food as Biological Oxygen Demand (BOD) in kg to the mass of the microorganisms in the process as Mixed Liquor Suspended Solids (MLSS) in kg.

 

Maintain WWTP at 100% loading

This option requires acquiring a solution to feed the biomass during the downtime. Acetic acid, sodium acetate and molasses are examples of chemicals used as a BOD source. The BOD concentration of these solutions will usually be several orders of magnitude stronger than the usual wastewater so to ensure the correct BOD loading in kg/day only a small volume of the solution is required via a drip feed or dosing pump. Most of the environmental services of chemical supply companies will stock these or other solutions which may have Nitrogen and Phosphorus at the optimum 100:5:1 ratio for biomass. After a few weeks on one of these solutions, your biomass will be able to pick up right where it left off as the f:m ratio hasn’t changed throughout the downtime.

 

Allow loading drop to 10-25% while keeping the biomass healthy

This option is more economical than keeping the WWTP at 100% as it is not necessary to import as much artificial feed but requires more management. The idea is to keep the f:m ratio relatively stable with a gradual reduction of no more than 10-20%. So the f:m ratio won’t change much, but the feed or the loading will drop significantly, therefore the mass of biomass or MLSS has to drop. Biomass must be removed from the system as waste sludge, this means there is less biomass to feed. Reducing the MLSS in the system will take several days depending on the type of WWTP in question. Then when it is time to get back up to 100% loading, biomass must be retained to build back up the MLSS. Depending on the system this will take 2-5 days.

This option can be considered the damage limitation option. You want to try to avoid losing the biomass and having to reseed the WWTP but the costs of importing feed makes it hard to justify keeping the loading at 100% or close to it. By reducing the quantity of biomass in the process, the contents of the balance tank could be used to drip feed the process for some time and minimal if any imported feed would be required. The loading may also be much lower for some time, if production drops to 10-25% for the foreseeable future the WWTP may have to deal with that even though it was not designed to. Depending on our client’s requirements we will design a WWTP with a turndown ratio of up to 8:1 meaning the WWTP will treat wastewater nearly as efficiently at 12.5% load as at 100% load. Not all WWTPs can sustain being turned down to this level but usually minor changes can increase the turndown ratio significantly.

 

Allow Biomass die and reseed when possible

This option is hard to advise but may be a reality for many businesses especially the smaller WWTPs associated with tourism, sport and other facilities which won’t have the same footfall for some time. This may seem a cheap option in the short term and maybe the only option for some but after the WWTP is shut down and it comes time to start it up again seed biomass will be imported from a healthy WWTP. The start-up time and costs will be significant if starting from scratch, to try and reduce these we would advise certain pieces of equipment to be left running to avoid any damage. The aeration system if using piped air should be left running at a reduced rate to avoid liquid ingress and to avoid septicity. Mixers should be operated intermittently to avoid solids setting and going anaerobic which can lead to hydrogen sulphide emissions. Also, scums can create hard floating layers or foul instruments if mixing is turned off completely. The process of reseeding can be complicated especially with more advanced wastewater treatment processes such as Nitrite shunt, Enhanced Biological Phosphorus Removal or Annamox.

There is a lot to think about during these unprecedented times we live in. Hopefully, these options can help avoid issues with WWTPs, and give some guidelines for when production facilities are up and running again at full capacity. Future production could look very different as restrictions are gradually lifted, which could require WWTPs to operate in a new capacity with different organic loading requirements.

 

Wastewater Treatment Services

We will be working from home for the foreseeable future and visiting sites only where completely necessary, as per government guidelines. WEW Engineering are members of ACEI and Engineers Ireland, we are offering free consultations concerning the issues above or any other issues relating to Water, Energy and Wastewater.

COVID-19, Advisory Services

Our people and our clients are our priority at WEW Engineering

While our offices will remain open, we are advising our staff to work from home, where possible, as per Government guidance with business continuing as normal.

All our staff members are fully contactable and fully available as required, via phone or email. Through our IT structure, we have the ability to work from home and can securely access our systems remotely.

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The application of Short Cut Nitrogen Removal in Industrial Wastewater Treatment

Introduction

To date short cut nitrogen removal has been limited to the treatment of side stream flows from filtrate or centrate of anaerobically digested wastewaters, sludges, and landfill leachates. These flows have high ammonia levels and low levels of biodegradable COD. Traditionally biological nitrogen removal on mainstream wastewaters is achieved by nitrification and denitrification. This process is now well established and the modified Ludzack Ettinger process is most commonly used. There are however many industrial wastewaters that are high in total nitrogen relative to the amount of biodegradable COD and in these cases, there may not be enough biodegradable COD to achieve full nitrogen removal by the traditional process. However, it may be possible to use some of the other nitrogen removal paths that use less biodegradable COD and require less oxygen. This paper reviews how we can improve nitrogen removal by enhancing conditions to favour the short cut nitrogen routes.

 

Theoretical Background

Conventional Nitrification and Denitrification

 

The conventional nitrification and denitrification process for nitrogen removal utilises autotrophic bacteria in an aerobic environment to convert ammonia to nitrite then to nitrate. This is done by ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) respectively. Heterotrophic bacteria in an anoxic environment then convert the nitrate back to nitrite before converting the nitrite to nitrogen gas. This process relies on the addition of a lot of oxygen (energy) and carbon (BOD), it also produces a lot of sludge or volatile suspended solids (VSS).
The Modified Ludzack-Ettinger (MLE) process is designed to use nitrate produced by the aeration zone as an oxygen source for hetrotropic bacteria in the breakdown of raw wastewater in the anoxic basin. The influent wastewater return sludge from the clarifier, and nitrate-rich mixed liquor pumped from the effluent end of the aeration tanks are mixed together. The influent wastewater serves as the carbon source for bacteria, return activated sludge from the clarifier provides microorganisms, and the anoxic recycle pumps provide nitrate as an oxygen source. The anoxic basin is mixed, but not aerated.
The (MLE) process employs the conventional nitrification and denitrification process for nitrogen removal mention above.

Modified Ludzack-Ettinger process

Figure 1. Modified Ludzack-Ettinger process; source: Minnesota Pollution Control Agency, 2010.

 

Advantages

The MLE process is relatively simple to control, maintaining the DO level in the aerobic zone is usually sufficient. The nitrate recycle and subsequent use of nitrate as an oxygen source reduces the oxygen requirements. The process will do more than just convert nitrogen compounds into nitrogen gas, the fact that it will produce a larger quantity of biomass than the nitrite shunt process means that soluble carbon, nitrogen and a small amount of phosphorus compounds will be converted into solid biomass which will, in turn, be separated in the clarifiers.

 

Suitability and Justification

In the MLE process, the anoxic tank is normally smaller than the aeration tank and the nitrate recycle flow is normally up to 5 times the raw wastewater flow.
The aeration tank is used to remove the last of the soluble BOD, and to convert the ammonia to nitrate.
In general, this process is only suitable for handling inlet nitrogen concentration of less than 100 mg/l.

 

Short Cut Nitrogen Removal

If the correct conditions can be created to favour the AOBs and inhibit the NOBs the nitrate stage of the process outlined above can be skipped. This is called nitritation-denitritation or more commonly as nitrite shunt (NS).
Although the biological denitrification takes place without extra oxygen being delivered, delivery of oxygen to the anoxic reactor at a reduced rate of the demand (50% to 70%), also referred as to aerated anoxic, leads to the process performance improvement. The NS may be followed by a second tank, where final simultaneous nitrification-denitrification (SND) polishing takes place to reduce ammonia, oxidised nitrogen and COD levels below licence limits.

 

Nitrite Shunt – Polishing Reactors – De-ammonification

 

Nitrite shunt process

Figure 2. Nitrite shunt process.

Advantages

Skipping the nitrate stage reduces the oxygen and carbon requirements as well as reducing the sludge production.
• The nitrite shunt design will reduce the COD requirement for nitrogen removal by up to 40% compared to conventional nitrification and denitrification.
• The nitrite shunt design will reduce the oxygen required for nitrogen removal by up to 25%.
• The nitrite shunt will provide up to 40% reduction in the biomass production associated with denitrification.

 

Suitability and Justification

The nitrite shunt process requires more advanced process controls to create the optimum conditions for the AOBs and to, therefore, get the best ratio of AOB to NOB. The advantages listed above are very attractive especially if the raw wastewater is pre-treated using anaerobic digestion which removes a large portion of the carbon to produce biogas a renewable energy source.

 

The Nitrite Shunt and De-ammonification

It should be noted that it is also possible to convert ammonia direct to nitrogen gas using nitrite and the presence of Anommox bacteria. To date, this has been developed successfully by a number of specialist companies but again only for sidestream flows.
Theoretically, the nitrite shunt step and the de-ammonification step can be combined to allow removal of ammonia without the consumption of any carbon or biodegradable COD and with virtually no excess sludge production. This combined process step is available from a number of specialist companies. Patented and branded processes include:
• The DEMON SBR Process by DEMON Switzerland
• The SHARON Process by Sweco and Delft University
• The DeAmmon Process by Purac/Lacekby
• The ANITA Mox Process by Veolia
• The Cleargreen Process by Infilco Degremont
It is, however, possible to use standard process design and engineering to create conditions that will achieve the nitrite shunt process without the growth of Anommox bacteria.

 

Mainstream Nitrite Shunt Process Design and Control

 

Hydrolysis

The wastewater must be preconditioned to ensure that organic nitrogen is hydrolysed to ammonia. This often happens automatically in upstream sumps or balance tanks. This is a precondition for the removal of all organic nitrogen in all biological processes (all conventional plants).

 

Reactors and Clarifiers

As a minimum two main reactor tanks and a final clarifier are required to operate in series as shown.

Nitrate Shunt and Polishing Reactors

• The first reactor tank operates as the Nitrite Shunt Reactor.
• The second reactor tank operates as a polishing reactor.
• A Nitrite shunt clarifier may be added to separate the biomass and reduce the return of nitrite oxidising bacteria to the nitrite shunt reactor.

 

Process Control

The process performance relies on creating conditions that ensure the nitrite oxidising bacteria (NOB) are suppressed so that nitrite is not converted to nitrate in the first reactor.
Control parameters that help to suppress the growth of NOB bacteria in the nitrite shunt reactor are as follows:

Dissolved Oxygen: This should be maintained below 0.5 mg/l in general.

Reactor liquid temperature: The process is better suited to reactor operating in the range of 20 to 35 degrees C.

Total Ammonia Nitrogen: Residual total ammonia nitrogen (TAN)(sum of ammonium and ammonia) should be maintained above 1.0 mg/l as the AOB growth rate drops if the substrate ammonium levels are too low.

Transient Anoxia: Alternating anoxic and aerobic conditions are required and can be created by turning aeration equipment on and off and by the use of multiple raw wastewater feed points that can be opened and closed. Oxidation Ditches may be used to naturally create anoxic and aerobic zones.

Solids Retention Time (SRT): Low SRT can assist with the washout of NOB.

Ammonia-based aeration control: This is the simplest form of process control

AVN (ammonia versus nitrate) control: This is a more advanced form of process control. It comprises the following; An aerobic duration controller, A dissolved oxygen controller to maintain the DO at a set point during the aerobic period, An ammonia sensor and an oxidised nitrogen sensor. The ratio of ammonia to oxidised nitrogen is maintained constant. Set points are set for timers and sensors to ensure satisfactory operation.

Shortcut Nitrogen Removal

Figure 4. Shortcut Nitrogen Removal—Nitrite Shunt and Deammonification. Publisher: Water Environment Federation

 

Microbiology and Laboratory Support

Our ability to identify the different bacteria has increased and two techniques are now available namely
Fluorescence in Situ Hybiridization (FISH)

Quantitative real-time polymerase chain reaction analysis.
These techniques can be used to confirm that the AOB bacteria are relatively abundant and that the NOB bacteria are suppressed. (pPCR).

 

Nitrite Shunt Application

While many new plants may benefit from a complete Nitrite Shunt and De-ammonification process step, many new and existing plants will benefit from the application of nitrite shunt process and downstream polishing reactors only.
It is especially suitable where the readily biodegradable COD to Nitrogen ratio is between 4.0 and 2.0 and where the wastewater temperature is above 20 °C.
There are many existing plants with multiple reactors tank that can be modified to improve the level of nitrogen removal.
Typical existing Industrial WWTPs include:

Dairy plants with an upstream anaerobic stage. Brewery plants with an upstream anaerobic stage. Pharmaceutical plants with high nitrogen levels. Landfill Leachate Plants.

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