Water Management in Biomass Processing

By Lorenz Bauer Ph.D, Lee Enterprises Consulting

“Water, water, everywhere, And all the boards did shrink; Water, water, everywhere, Nor any drop to drink.” Samuel Coleridge

Managing the water in biomass processes like food production, fermentations, pyrolysis, and biodiesel production is critical to success.   There is an increasing appreciation of the value of clean water. The value of water is related to its quality. Even locations with abundant supplies of fresh water have concerns involving potable water and waste disposal.    Water-related issues can be a show stopper. There are instances of completed projects being shut down due to issues with water disposal.  For many projects significant savings are possible by proper design and implementation.  Over 100 methods for water treatment are known.  They are often applied in combination and in multiple stages.  Advanced polishing steps are often required to produce pristine water.

The major bioeconomy processes including food processing, fermentation (including ethanol production), pyrolysis, and biodiesel production all have unique water treatment problems and opportunities for improvement.   Determining the most effective and economical methods of treatment requires expertise and experience.  With proper advice it is possible to avoid issues that have caused problems in the past and find opportunities to recoup value from wastewater.

Water Management Planning

The goals of a water management plan are straightforward:

1. Meet water quality requirements
2. Minimize capital and operational costs,
3. Comply with all regulations.
4. Be reliable and easy to operate with minimal attention.
5. Recover as much value as possible from material in the water
6. Minimize the amount of potable water used and discharged.

Managing the water used in biomass processing presents special challenges and opportunities.  Process water is often used as media for fermentation and chemical reactions as well as for transporting and washing products.   There are purity requirements for water used for biosynthetic and catalytic processes.   The aqueous waste streams can be contaminated with chemicals derived from the biomass or used in the process.  There are potential problems with microbes.   There are colloidal particles and dissolved metals ash that needs to be managed.  The metals are often found in organic complexes that resist traditional removal methods.

A significant amount of the carbon in the biomass is soluble in the water.    Capturing the value from aqueous product streams can be challenging.   Inefficient separation can significantly lower the fuel value of the product.    Some of the carbon is in the form of valuable chemicals.  Processes for separating these chemicals and recovering the carbon can significantly improve the economics of biomass processing.

Wastewater disposal is tightly regulated and proving that a new process does not increase the burden on the local environment and infrastructure can be challenging.  Regulators are very conservative and it is helpful to have a track record of success to convince them to accept novel plans.  Water issues can be used as a roadblock by groups trying to delay development efforts.

The first step in developing a water plan is to understand the process requirements via a detailed flow diagram showing all of the flow and flow rates, and including:

• Impurities in all of the sources of water including estimated concentrations.
• Methods for removing these impurities
• Concentrations of impurities that are added or concentrated in each process step.
• Chemicals needed to remove impurities or remediate the water
• The anticipated constituents of discharged water without treatment.

A detailed analysis of the streams is needed that goes beyond typical regulatory requirements.  A thorough understanding of the chemistry and biology of the process streams is needed to avoid major issues.    Fermentation processes are particularly sensitive to water quality and some catalytic processes are also highly sensitive. There have been examples of rapid microbe die offs and catalyst deactivation by contaminants in the water.

Water Sources

It is important to consider all of the water used in a facility.  In addition to the water used in the pretreatment and processing of the biomass, there are several other water uses that need to be considered.  These include steam production, cooling towers, potable water, human wastes, firewater protection, and the sewage system.  There may also be side processes that require water.  Each of these uses has its own specifications depending on temperatures, hardness, corrosivity and specific constitutes. Drinking water, shower water, and eyewash water must meet potable water requirements.

One item that is often forgotten is the need to collect and treat storm run-off water that has contacted storage areas and equipment.   A plant can be held responsible for insuring the quality of this run off water even if it is better than the ground water from the surrounding areas.

Water sources can have unrecognized issues.  The level of dissolved solids can meet drinking water standards but not the standards required for the process.   The surface water source changes dramatically seasonally making pretreatment equipment selected ineffective for much of the year.  There are times when local ground and river water already exceed the standards for new industrial discharges.  The local water authority treatment plants can be close to capacity and there can be no capacity for new sources of influent.   Biological oxygen loading is sometimes overlooked, and can be too high for direct discharge into local rivers.

Water Treatment Plan Requirements

A fully integrated plan will address many issues:

1. Available source(s) of water: municipal, well, surface and other

• Complete analysis of water properties.
• Seasonal variations & reliability of supply.
• Cost of water.

2. Plant unit operations, water uses, and volume required.

• Overall water balance for plant.
• Water source’s ability to supply the required volume.
• Opportunities for reuse of the water in the plant.

3. Recovery of valuable components in the water

• Chemicals
• Metals
• Carbon
• Nutrients

4. Technologies available that are reasonably applicable to the specific site.

• Clarification.
• Traditional filtration technologies.
• Ion exchange.
• Membrane technologies. (Microfiltration, ultrafiltration, nanofiltration, and osmosis, etc.)
• Biological Digestion.
• Novel technologies

4. Available discharge of wastewater should be determined even if there are design efforts for zero liquid discharge.

• Publicly Owned Treatment Works (POTW).
• Direct discharge to lake or stream.
• Evaporation.
• Need for advanced polishing steps to produce pristine water

5. Impact of utility costs on water management options.

• Acquisition & discharge of water.
• Cost of fuel and/or electric energy.

 Food Processing

Food processors are under continuing pressure to improve their sustainability, particularly in regards to water use and discharge.   Economics often requires that they be located close to production and distribution points that may have water restrictions.   The straightforward way of disposing of the waste produced is just to release them into nearby water-bodies or to convenient open land. But, now it has become almost impossible to practice that measure due to increased population, increased industrial development, and awareness of the damage caused by pollution.   This has led industries to treat water prior to release.

An example of this is the potato processing industry which uses copious amounts of water.  The raw potatoes from the field need to be cleaned first.   The scrubber removes field residues, stones, and other extraneous matter.   The resulting wastewater contains both organic loads and a high load of silt and sand. Wastewater from the subsequent peeling process mainly contains peeling residues.  Metals are extracted from the potatoes and concentrated in the water.   If hot water is used in pre-treatment such as cooking or blanching, swelled starch is added to the wastewater.   Process water can also have a high content of microbes that must be addressed.   If the potatoes are fried, the process adds oil, organic carbon, and pyrolysis products.   Reuse of the water in the process often requires that it meets drinking water standards.   There are also issues with heat recovery.   These factors present a complex water management problem requiring sophisticated and expensive multiple step treatments.   There is a desire to lower the net water used and to find lower cost methods of disposal.

Fermentation and Ethanol Production

Fermentation processes including ethanol production generally do not produce effluents containing toxic materials that are an acute health risk.  Unfortunately, effluents of fermentation do contain many toxicants that affect the flora and fauna by reacting with microbes and drastically decreasing the dissolved oxygen levels of that area.   The effluents can be treated by oxidative ponds (lagoons), spray irrigation, well disposal, and incineration.  Removing solids from the wastes is typically done by physical treatments such as filtration, sedimentation, or centrifugation.  Chemical treatments are used to aid flocculation and coagulation for solids removal.  These include ferric sulphide, calcium hydroxide etc.   Other treatments used include treatment trickling filters, biologically aerated filters, and rotating biological contactors.   These are often used with activated sludge, aerobic and anaerobic digesters, anaerobic filters, up-flow anaerobic sludge blankets, and other anaerobic treatment processes.

In a corn ethanol production plant, ethanol is distilled, and whole stillage, which is the residue of enzymatic hydrolysate of corn fermentation mixture, is usually centrifuged to produce a liquid fraction (thin stillage) and a solids fraction (wet distillers’ grains).   Thin stillage has a high water content.  Processing of thin stillage with conventional methods (evaporation and drying) is energy intensive. Anaerobic digestion can be applied to improve the energy balance of the process since the biogas produced presents an alternate energy source.  Developing methods capable of generating new value-added products from the thin stillage stream offers an opportunity to add more positive cash flow to the equation, independent of corn prices. Thin stillage is a potential source for several value-added bio-based products that include phosphorous, fatty acids, and char.

Pyrolysis for Fuel and Chemicals

Biomass pyrolysis has the potential of generating fuels and chemicals. The technologies practiced include slow pyrolysis, fast pyrolysis, fast pyrolysis with downstream fractionation, in situ catalytic fast pyrolysis, and ex situ catalytic fast pyrolysis. As the technology has developed, many new unit operations have been proposed ranging from hydrothermal treatment to advanced gasification.    These processes generate a unique collection of complex aqueous streams that contain solubilized organic compounds.  These compounds are often slated for wastewater treatment, creating an economic burden on the biorefinery.    From 12 to 300 g per Kg of organic carbon has been observed in such effluents; recovering value from these streams is the main route to improve the economics of the processes.   There are methods for recovering phenolics and organic acids in commercially interesting quantities.  Concentration of the carbon materials provides a stream that can be condensed or reformed into large molecules for use as fuels and other products.    The effluents generated after the extraction process will need to be evaluated and potentially treated.

Biodiesel Production

Production of biodiesel from plant oils produces wastes containing emulsified oil (biodiesel residual), glycerin, methanol, and soap screening.  Current approaches for treating the water include in-situ flocculation and advanced bioreactor treatment.    Membrane bioreactor polishing is needed as a post treatment to produce water that can be released to the environment.   However, there are many methods that can improve material recovery like a dissolved air flotation (DAF) wastewater treatment system to reclaim more of the resources

Conclusion

Skilled professionals with experience in technology evaluation, engineering design, project management, and regulatory issues are needed to evaluate the process needs.  There is a need to extract as much value from the aqueous waste streams as possible.  Solutions often combine biological, chemical, and physical methods.   These include traditional approaches like filtration, distillation, aerobic and anaerobic bioprocesses, extraction, distillation, and, osmotic polishing.   A deep understanding of biomass processing methods is needed particularly in cases where reuse of the water is planned.   Each technology may require a unique design.   The goal is to produce waste water than can be reused in the process or released to the local environment or water treatment systems at the lowest possible cost.

About the Author

Lorenz Bauer is a process chemist with experience designing and implementing new methods for producing platform chemicals, oil refining, and biomass conversion.   He is an independent consultant affiliated with Lee Enterprises Consulting’s water treatment, renewable chemicals, and emerging technology divisions.  He earned his Ph.D. at Washington University working with phenolic resins.   An inventor on 25 patents and author of over 20 publications, his projects have ranged from food additives, off gas treatment, upgrading unconventional feeds and to waste recycling.   Several of these technologies were commercialized.  Most recently he worked on developing fuels and chemicals from renewable.  He is Six-sigma black belt trained in project management.  He is based in Houston evaluating new technologies in biomass conversion, renewable chemicals, catalysis and material science.