• Nutrient Supplementation Strategies
    for AD and RNG Projects
    At Celignis Biomass Lab

Why Nutrients are Important to Digester Performance

Nutrients are essential for maintaining stable microbial populations and for efficient enzymatic activities throughout the four stages (hydrolysis, acidogenesis, acetogenesis, and methanogenesis) of anaerobic digestion. Certain trace elements, such as iron and selenium are also useful in combating the toxic effects from H2S, volatile fatty acids (VFAs), and ammonia. Trace elements can also help in increasing the organic loading by increasing the overall kinetics of anaerobic digestion.

Each element has its role in microbial metabolism during anaerobic digestion and limitation of even a single element can cause process imbalances and decreases in process efficiency. Trace elements limitations can be mostly seen by VFAs accumulation and reduced biogas production.


Lack of trace elements usually occurs in mono-digestion, but can also occur in digesters processing multiple feedstocks (co-digestion). Testing for trace-elements in the feedstock and the digester can indicate which elements are lacking and can allow for a strategy where supplementing with these limited trace elements will improve the process stability and efficiency.

Bioavailability is a key parameter to consider while designing the mix of trace elements. They should be soluble and should not form precipitates such as sulphides and carbonates. Also, the amount of chlorides and sulphates added to the digester in the form of trace element salts should be controlled carefully.

Excessive use of trace elements leads to inhibition. Hence, the feedstock should be analysed for trace elements and only the required elements at the required concentrations should be supplemented.


How We Can Help with Nutrient Supplementation Strategies


We can suggest optimal values for the presence of major and minor elements in the digester as well as upper and lower threshold values.

For elements considered to be of major importance to reactor performance, in cases where the concentrations are below the recommended minimum values we would advise supplementation of these elements.

This allows us to formulate a bespoke cocktail of additives, designed according to the specific requirements of the digester.

Such custom cocktails are more likely to address digester peformance issues than off-the-shelf nutrient mixes.


We can work with your own data on the nutrient contents in your feedstock and digester or we can undertake the analysis of major and minor elements of samples in our laboratories.

We can also test the effects of nutrient supplementation in lab-scale experiments whereby the strategy is compared against the control in our biomethane potential tests. Additionally, nutrient supplementation approaches can be tested in continous digestions, lasting three months or longer, undertaken in our laboratories using reactors up to 12 litres in volume.

Case Study on Nutrient Supplementation

A Germany-based biogas company that operates dozens of AD/RNG plants in Europe and the UK approached Celignis to support them in optimising their plant operations to allow for more consistent outputs and reduced downtime. As a result, Celignis provided Biological Consultancy support which involved us analysing the plant process data in terms of: feedstock loading (organic loading rate); recirculation strategies; biogas composition and yield; volatile fatty acids (VFAs); and alkalinity.

This detailed analysis of the plant process data allowed us to provide operational limits and indicators in the plant beyond common indicators such as VFA and alkalinity and acetic acid to propionic acid ratios (isoforms of volatile fatty acids, presence of traces of hydrogen in the biogas, Hydrogen sulphide and ammonia) and provided green, yellow and red zones for each of the indicators.

In addition to this, Celignis also developed a tool for the company to allow self-design of major and minor elements (nutrients) for the biogas plants based on the feed chemical composition. The tool was designed to be suitable for mono and co-digestion and allows for change from one feedstock to other, and for addition of a new feedstock to the co-digestion mix, without there being a negative affecting on plant performance.

Click here for more information on our Biological Consultation services for the anaerobic digestion/RNG sector, here for information on our Process Optimisation services, and here for information on our analyses of Process Parameters.

Additional Information on Nutrient Supplementations

Feel free to get in touch with us if you have any questions about our services to recommend nutrient supplementation strategies or if you are looking to address issues that you are experiencing with your current digester performance. Relevant members of the Celignis anaerobic digestion team will be happy to assist. Those team members with the most experience with undertaking these tests and interpreting the resulting data are listed below.

Lalitha Gottumukkala

Founder and Lead of Celignis AD, CIO of Celignis

PhD

Has a deep understanding of all biological and chemical aspects of anaerobic digestion. Has developed Celignis into a renowned provider of AD services to a global network of clients.

Kwame Donkor

AD Services Manager

BSc, MSc, Phd (yr 4)

His PhD focused on optimising AD conditions for Irish feedstocks such as grass. Kwame is now leading the Celignis AD team in the provision of analysis and bioprocess services.

Sajna KV

Bioanalysis Developer

PhD

Our Biomass Detective! Designs, tests, optimizes and validates robust analytical methods for properties of relevance to the anaerobic digestion sector.



Other Celignis Tests and Services for Anaerobic Digestion

Global Recognition as AD/RNG Experts

Celignis provides valued services to over 1000 clients. We understand how the focus of AD projects can differ between countries and have advised a global network of clients on their RNG projects. We also have customs-exemptions for samples sent to us allowing us to quickly get to work no matter where our clients are based.

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Biomethane Potential

The biomethane potential (BMP) can be considered to be the experimental theoretical maximum amount of methane produced from a feedstock. In our laboratory, we have six BMP systems, comprising 90 reactors, that allow us to digest your samples and determine the biogas yield over periods of between 14 and 40 days.

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Continuous Digestions

To help you evaluate how well your anaerobic digestion feedstocks will behave in real-world conditions we can undertake continuous digestion experiments. These operate at scales up to 12 litres and typically run for 3 months. We target maximum achievable organic loading rate (OLR) and biomethane potential.

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Toxicity Assays

The waste streams used in AD that arise from process industries may contain toxic or bacterial inhibitory compounds (e.g. antibiotics, polyelectrolytes, detergents). Our anaerobic toxicity assays can determine the presence of such toxicities and suggest the feeding limits for feedstocks.

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Process Optimisations

There a many factors to consider when running an AD facility. We can design and experimentally-validate optimisations of these factors at the lab-scale prior to you implementing them at your AD facility. Such an approach allows for greater benefits and lower costs than optimising the process at the commercial scale.

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Feedstock Analysis

Our analysts have characterised tens of thousands of biomass samples. We have dedicated analyses packages for the compositional parameters of most relevance to AD/RNG. Additionally, based on our detailed analyses we can recommend appropriate feedstock mixing proportions in co-digestion facilities.

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Biological Consultations

We're experts in the biology of anaerobic digestion. We pour through operational data from biogas plants and identify correlations between process parameters and plant performance. This understanding on the specific biology of the digester allows for recommendations as to how peformance can be improved and made more stable.

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Specific Microbial Activity

AD is a microbial process involving a sequence of stages (hydrolysis, acidogenesis, methanogenesis) to convert a complex feedstock to methane. We analyse samples collected from digesters and undertake tests to investigate how well they proceed with each of these stages of digestion.

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Technoeconomic Analyses

Our TEA experts work with you to evaluate the economic prospects of your AD/RNG facility, considering various scale, technology, and feedstock options. We apply accurate costing models to determine CAPEX/OPEX of simulated and pilot scale processes which are then used to determine key economic indicators (e.g. IRR, NPV).

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Digestate Analysis

Digestate is the residue after the anaerobic digestion process. It can potentially have value as a soil fertiliser. We offer a range of detailed analysis packages for digestate, allowing you to fully assess this resource and to determine the best use for it. Our team can also assist in evaluating digestate valorisation options.

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Project Development

The criteria for the development of a successful AD project are numerous and vary according to region, technology, and feedstock. We have a deep understanding of these regional, technical, and biological differences and have advised a global network of clients on effectively developing their AD projects.

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Process Parameters

Celignis can undertake a range of key analyses for KPIs and advanced process monitoring. These include volatile fatty acids (VFAs); Alkalinity ratio (FOS/TAC); and redox potential. It is particularly imporant that these are monitored when undergoing changes of feedstock type, organic loading rate and hydraulic retention times.

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Publications on Anaerobic Digestion By The Celignis Team

Ravindran, R., Donkor, K., Gottumukkala, L., Menon, A., Guneratnam, A. J., McMahon, H., Koopmans, S., Sanders, J. P. M., Gaffey, J. (2022) Biogas, biomethane and digestate potential of by-products from green biorefinery systems, Clean Technologies 4(1): 35-50

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Global warming and climate change are imminent threats to the future of humankind. A shift from the current reliance on fossil fuels to renewable energy is key to mitigating the impacts of climate change. Biological raw materials and residues can play a key role in this transition through technologies such as anaerobic digestion. However, biological raw materials must also meet other existing food, feed and material needs. Green biorefinery is an innovative concept in which green biomass, such as grass, is processed to obtain a variety of protein products, value-added co-products and renewable energy, helping to meet many needs from a single source. In this study, an analysis has been conducted to understand the renewable energy potential of green biorefinery by-products and residues, including grass whey, de-FOS whey and press cake. Using anaerobic digestion, the biogas and biomethane potential of these samples have been analyzed. An analysis of the fertiliser potential of the resulting digestate by-products has also been undertaken. All the feedstocks tested were found to be suitable for biogas production with grass whey, the most suitable candidate with a biogas and biomethane production yield of 895.8 and 544.6 L/kg VS, respectively, followed by de-FOS whey and press cake (597.4/520.3 L/kg VS and 510.7/300.3 L/kg VS, respectively). The results show considerable potential for utilizing biorefinery by-products as a source for renewable energy production, even after several value-added products have been co-produced.

Donkor, K. O., Gottumukkala, L. D., Lin, R., Murphy, J. D. (2022) A perspective on the combination of alkali pre-treatment with bioaugmentation to improve biogas production from lignocellulose biomass, Bioresource Technology 351

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Anaerobic digestion (AD) is a bioprocess technology that integrates into circular economy systems, which produce renewable energy and biofertilizer whilst reducing greenhouse gas emissions. However, improvements in biogas production efficiency are needed in dealing with lignocellulosic biomass. The state-of-the-art of AD technology is discussed, with emphasis on feedstock digestibility and operational difficulty. Solutions to these challenges including for pre-treatment and bioaugmentation are reviewed. This article proposes an innovative integrated system combining alkali pre-treatment, temperature-phased AD and bioaugmentation techniques. The integrated system as modelled has a targeted potential to achieve a biodegradability index of 90% while increasing methane production by 47% compared to conventional AD. The methane productivity may also be improved by a target reduction in retention time from 30 to 20 days. This, if realized has the potential to lower energy production cost and the levelized cost of abatement to facilitate an increased resource of sustainable commercially viable biomethane.

Donkor, K. O., Gottumukkala, L. D., Diedericks, D., Gorgens, J. F. (2021) An advanced approach towards sustainable paper industries through simultaneous recovery of energy and trapped water from paper sludge, Journal of Environmental Chemical Engineering 9(4): 105471

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This study considered the possibility of reducing the environmental footprint of paper and pulp industry by producing bioenergy from paper sludge by using process wastewater instead of fresh water, and reclaiming water trapped in paper sludge. Experimental studies are conducted with streams from three different pulp and paper mills (virgin pulp mill (VP), corrugated recycling mill (CR), tissue printed recycling mill (TPR)) for sequential bioethanol and biogas production with simultaneous reclamation of water from paper sludge (PS). Total energy yields of 9215, 6387, 5278 MJ/tonne dry PS for VP, CR and TPR, respectively, were obtained for ethanol-biogas production. Virgin pulp paper sludge gave the highest yield for ethanol and biogas in stand-alone processes (275.4 kg and 67.7 kg per ton dry PS respectively) and also highest energy conversion efficiency (55%) in sequential process compared with CR and TPR. Energy and environmental case study conducted on virgin pulp mill has proven the possibility of using paper sludge bioenergy to reduce energy demand by 10%, while reclaiming 82% of the water from the PS, reducing greenhouse gas emissions (GHG) by 3 times and producing solids suitable for land spreading.

Gottumukka L.D, Haigh K, Collard F.X, Van Rensburg E, Gorgens J (2016) Opportunities and prospects of biorefinery-based valorisation of pulp and paper sludge, Bioresource technology 215: 37-49

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The paper and pulp industry is one of the major industries that generate large amount of solid waste with high moisture content. Numerous opportunities exist for valorisation of waste paper sludge, although this review focuses on primary sludge with high cellulose content. The most mature options for paper sludge valorisation are fermentation, anaerobic digestion and pyrolysis. In this review, biochemical and thermal processes are considered individually and also as integrated biorefinery. The objective of integrated biorefinery is to reduce or avoid paper sludge disposal by landfilling, water reclamation and value addition. Assessment of selected processes for biorefinery varies from a detailed analysis of a single process to high level optimisation and integration of the processes, which allow the initial assessment and comparison of technologies. This data can be used to provide key stakeholders with a roadmap of technologies that can generate economic benefits, and reduce carbon wastage and pollution load.

Gottumukkala L.D, Parameswaran B, Valappil S.K, Pandey A (2014) Growth and butanol production by Clostridium sporogenes BE01 in rice straw hydrolysate: kinetics of inhibition by organic acids and the strategies for their removal, Biomass Conversion and Biorefinery 4(3): 277-283

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Growth inhibition kinetics of a novel non-acetone forming butanol producer, Clostridium sporogenes BE01, was studied under varying concentrations of acetic and formic acids in rice straw hydrolysate medium. Both the organic acids were considered as inhibitors as they could inhibit the growth of the bacterium, and the inhibition constants were determined to be 1.6 and 0.76 g/L, respectively, for acetic acid and formic acid. Amberlite resins—XAD 4, XAD 7, XAD 16, and an anion exchange resin—Seralite 400 were tested for the efficient removal of these acidic inhibitors along with minimal adsorption of sugars and essential minerals present in the hydrolysate. Seralite 400 was an efficient adsorbent of acids, with minimal affinity towards minerals and sugars. Butanol production was evaluated to emphasize the effect of minerals loss and acids removal by the resins during detoxification.





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