Environmental Engineering Blog

A MSW landfill generates two types of wastes: leachates, which are effluents containing contaminants produced from rain percolating through solid wastes, and biogas, which is produced as a result of chemical reactions of solid wastes buried in the landfill.

All MSW landfills are required by law to treat both types of wastes, so in this post we will see how biogas can be recovered and reused as an energy source for the treatment of leachates, without incurring huge costs, which would be involved in the transformation of biogas into energy or fuel for other uses.

Is biogas energy recovery profitable?

The energy resulting from biogas transformation can be reused for two main purposes:

1. To generate electrical and thermal energy. This process can be carried out by motor-generator units, or biogas turbines.

2. To be directly used as fuel after purification, serving as:

• Fuel for biogas boilers.
• Injection into natural gas network.
• Automotive Fuel.

The challenge faced by most MSW landfills is that the installation of the machinery necessary for the transformation of biogas into energy or fuel is too costly and, above all, unprofitable. This is because the amount of biogas generated in most landfills is not enough to produce a really significant amount of energy that can be reused to offset the investment made in machinery.

On the other hand, it is frequently the case that even when landfills  are capable of producing large amounts of electrical energy, no electricity transmission towers are located nearby to which the  generated energy can be transferred.

A possible solution to this would be not to transform biogas, but to burn it using flares instead, so that it is not emitted into the atmosphere. However this would not be the most appropriate choice, since this source of energy would be wasted.

A smarter solution for those landfills that do not generate a large volume of biogas would be to reuse it as a   source of energy to drive the landfill processes.

The biogas as an energy source for leachate treatment

There are several technologies that can be applied to MSW landfill leachates treatment,  however  the method of vacuum evaporation, combined with or without pre- or post- reverse osmosis, has proven to be nowadays the most efficient to minimize leachate  and obtain purified water suitable for discharge.

The energy needed by the vacuum evaporator to function may come from the landfill’s biogas. The use of a simple and economic system, such as a boiler with a biogas burner, will make it possible to obtain sufficient energy to ensure the proper functioning of the evaporator.

In this way, the benefits are threefold:

1. A source of energy is reused.

2. The energy required to operate the vacuum evaporator, intended to treat the leachate, is obtained at zero cost.

3. Biogas is reused by a much more profitable method in the case of landfills which do not generate biogas in sufficient quantities to justify the huge investment involved in its transformation into electricity, thermal energy or fuel.

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Landfill biogas, landfill, leachate treatment, leachates, vacuum evaporation, vacuum evaporators

Each type of reactor produces  a different kind of waste stream, which differs in terms of their activity content and the produced amount of wastewater.

These active wastewater result from the purification of primary refrigerants (PWR, BWR), and the cleaning of the spent-fuel storage pool, washing water and water leaks. In addition, reactors decontamination operations also produce wastewater.

The resulting radioactive wastewater generally contains soluble and insoluble radioactive compounds and non-radioactive substances. The goal is to decontaminate wastewater to the extent that the total volume of the eflluent decontamination can be either released into the environment or recycled. Thereafter, waste concentrates undergo a process of conditioning, storage and disposal.

Standard techniques are commonly used to decontaminate liquid waste streams. Each process has a particular effect on the radioactive content of the effluent. The best results in volume reduction, compared with other techniques, are achieved by means of vacuum evaporation.

Vacuum evaporation is a proven method for radioactive wastewater treatment that provides both good decontamination and volume reduction results. The vacuum evaporator removes process water in the vapor phase, remaining only non-volatile components, such as salts containing most of the radionuclides. Evaporation is probably the best technique for wastes with a relatively high salt content and heterogeneous chemical composition.

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Power generation nuclear power plants, vacuum evaporation, vacuum evaporator, Wastewater treatment

Condorchem Iberica has been awarded the tender to carry out the second phase of capacity expansion of the municipal solid waste (MSW) treatment plant in Segrià, the province of Lleida (Catalonia) in Spain.

A common problem facing MSW landfills, is the highly polluting and environmentally hazardous liquid effluents they generate: the leachates. These effluents originate as a result of waste organic matter degradation and decomposition as well as from rain percolating through such waste.

Consequently, MSW landfills generate dark and odorous liquid effluents characterized by a very high organic load, high conductivity and a large presence of metal ions as well as  by  high concentrations of ammoniacal nitrogen, which cannot be discharged without prior treatment.

The capacity expansion will serve two purposes: it will allow the  plant to treat a larger amount of wastes from several towns in the immediate vicinity of the landfill; and  on the other hand, it will improve the efficiency of the municipal waste treatment systems employed so that the results  comply with National and European regulations.

In this regard, it is noteworthy that the current leachate treatment system used at the MSW landfill can reduce liquid waste from 100 liters down to 50. With the new plant to be annexed to the existing one, the resulting fraction will be 25, which represents an important advance. In addition, these wastes will be sent to another plant outside the facility to complete the treatment, so as to reduce them to an inert paste-like consistency to make them appropriate for storage.

Although the initial choice was to use physicochemical and/or biological waste water purification treatments for this type of effluents, it will be necessary to develop and implement physical processes of concentration instead, which, in this case, will provide better efficiency and performance, so as to obtain the desired results.

The systems of vacuum evaporation, combined with or without pre- or post- reverse osmosis  are specially indicated, since they produce high leachate reduction rates as well as purified water suitable for discharge, even under the most stringent limits by means of  a simple and cost-effective method.

Additionally, the biogas generated at landfills may be reused as a source of energy supply to the vacuum evaporation system, by means of either a boiler with a biogas burner or cogeneration systems.

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Landfill effluent, landfill, leachates, reverse osmosis, vacuum evaporation, vacuum evaporators, Wastewater treatment

Medium-density fiber (MDF) boards are wood fiber agglomerates, which are mainly used for furniture manufacture. This product has been on the increase for years, given its high resistance, stability and quality finish coupled with reasonable costs.

In brief, the MDF boards manufacturing process involves the removal of barks from tree trunks, which are shredded to obtain fibers that are agglomerated together with synthetic resins through high heat and pressure.

This process generates effluents containing fiber residues and various chemicals found in wood, as a result of the humidity in wood trunks, which can range between 1% and 15% in dry conditions. These are effluents with high levels of solid contents and chemical oxygen demands (COD’s).

A very common process in the sector includes effluent purification by physicochemical means. The problem is that the resulting water cannot be discharged, since its COD levels are not low enough. A solution that some manufacturers have tried in order to dispose of this water is throwing it into the ovens in which the boards are treated, so that it evaporates in the high heat. This, however, has not proven to be an efficient solution, since it leaves residues and stains on the boards.

Without any doubt, the most suitable alternative for the treatment of effluents generated in the MDF boards manufacturing process is vacuum evaporation, given it allows the reuse of both evaporation rejects (distilled water and residue concentrate),   which leads to the achievement of zero discharge.

The effluent is effectively introduced into the vacuum evaporator, which separates water from its waste content (fibers and other wood chemical components) producing, as a result, distilled water, that can be sent to the boilers to generate vapor instead of being discharged, as well as a wood fiber concentrate and other components, which can be sent to the biomass boiler to be mixed with other materials to generate energy.

To complete the cycle enabling the reuse of resources, it must be noted that  any tree waste which is not used for the production of MDF boards (such as bark, branches, leaves, etc.) can be combusted  to produce the energy necessary to power the evaporator, which means that the installation of this solution will have near-zero  energy costs.

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wood & corck MDF boards, vacuum evaporation, vacuum evaporators, wastewater, Wastewater treatment, zero liquid discharge, ZLD

Most companies in the power generation sector, both conventional and renewable, need to produce and utilize large amounts of vapor, leading to extremely high water consumption. That is why they frequently have water and wastewater treatment plants (combined in different ways).

Water treatment plants are designed to transform the collected water for vapor production (raw water) into high-quality purified water (inflow water) to be used in production processes (mainly vapor boilers).

These treatment plants utilize different technologies, which are combined depending on the quality of the collected water, the most prominent being the following:

•    Physicochemical purification
•    Reverse osmosis
•    Resins or electro-deionization (CEDI)

Reverse osmosis and resins produce effluents as a result of water distillation, which makes it frequently compulsory for companies to also have a wastewater treatment plant.

Wastewater treatment plants can also be used to treat wastewater generated in the cooling towers, which are designed to cool down residual vapor from boilers for reuse, as well as to treat wastewater from spills and water rejections that occur accidentally.

All of these effluents are usually sent to a container for further management in the wastewater treatment plant.

Once the effluents have been treated, two options can be considered:

1.  Discharging the resulting water, which is not the best option except when the quality of the water obtained is not suitable for reuse in production processes.
2.  Not discharging the resulting effluent, so that water can be reused in production processes.

The decision to be made relies on the company, but irrespective of the chosen option, wastewater are required to be treated to satisfy zero liquid discharge requirements.

Zero discharge processes involve several stages, depending on the quality of the wastewater to be treated, among which the following can be noted:

• Chemical pretreatment to remove contents that may cause fouling in later stages.
• First concentration by membrane filtration. Since the salt concentrate will still be too liquid it will be required to be sent to a vacuum evaporator.
• Second concentration by vacuum evaporation. Although the salt content in the resulting effluent is in higher concentration, it needs to be sent to a crystallizer since it is still liquid.
• Crystallization to treat the salt concentrate obtained after evaporation, which is then ready to be sent to the waste management unit, before which a drying process may be conducted.

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Power generation crystallization, power generation, reverse osmosis, vacuum evaporators, Wastewater treatment, water treatment, WTP, WWTP, zero liquid discharge

Nowadays, companies and public bodies allocate large budgets to construct and exploit different types of waste treatment plants (such as purification, biomethanation, thermal drying, cogeneration, composting, and construction waste recovery or incineration plants).

Despite of their highly beneficial contribution to the environment, the waste recovery rate hardly ever reaches 100%.  That is why increasing efforts are being devoted today to total removal of wastes, though such a goal may seem utopian.  For this purpose, a waste management system known as “zero liquid discharge” is being championed by municipalities, governments and companies.

This approach arises from the fact that the volume of wastes and discharges that society generates today is increasing at excessive rates, which will make it difficult for nature to assimilate them, and thus the implementation of recycling measures are no longer sufficient. Such state of affairs also requires fundamental changes in the way materials are treated during production and consumption, aimed at recovery and reuse rather than disposal.

In that regard, vacuum evaporation is one of the most innovative and effective technologies for  water-based liquid industrial waste minimization and treatment, which is not only clean, safe and very versatile but also has very low management costs.

Some of the most important types of vacuum evaporators are the following: heat pump vacuum evaporators,  mechanical vapor compression vacuum evaporators, vacuum evaporators for high flow rates, and  multiple-effect vacuum evaporators powered by hot water.

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General heat pump vacuum evaporators, mechanical compression vacuum evaporators, multiple effect evaporators powered by hot water, vacuum evaporation, vacuum evaporators, wastewater, zero liquid discharge, ZLD

Brine is a water solution with a very high concentration of salt or sodium chloride. The term also applies to solutions with other salts. The  most common applications  known to consumers are  highway deicing or as refrigerant in the refrigeration industries.

However, the brine generated as waste in industrial processes is a difficult problem that industries are facing.  Its treatment poses numerous difficulties and purification of saline wastewater is not very effective by means of the technology usually employed:  physicochemical or biologic treatments, etc.

Different alternatives, such as membrane separation technologies, do not provide the desired results in the case of brine treatment. This is mainly due to the high amount of rejects  generated and the inconvenience caused by the presence of organic contaminants in  filtration membranes.

Therefore, vacuum evaporators have proven to be, by far, the most successful technology for the treatment of this type of wastewater. On the one hand, this system enables the highest degree of concentration possible, up to the point of salt drying up completely; and on the other, it generated purified effluents, which are compliant with usual discharge limits, because of their extremely low conductivity and organic contaminant contents.

The management of the concentrate is the most compromised aspect of the treatment. The aim is to  minimize it as much as possible in the most cost-effective way, as the final destination will be a waste manager unit (if it is a highly concentrated brine) or a landfill, if salt precipitation happens to occur.

In any case, vacuum evaporators already have a proven track record for effectively treating brines generated by the following industries:

• Food industry:

- Hams and prepared meat products
- Meats, canned fish and shellfish,  fish farms
- Pickles, olives and other pickled foods
- Lupines, pine nuts, almonds, and other canned vegetables
- Animal offal

• Chemical and pharmaceutical industry

• Leather tanning industry

• General industry: rejects from reverse osmosis

• General industry: eluates from decalcifier  regeneration

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General brines, brines concentration, brines treatment, vacuum evaporation, vacuum evaporators, wastewater

In recent years, products whose composition include natural organic additives, have experienced significant growth. Some examples of this type of products can be found in sectors such as cosmetics and natural medicine (aloe vera), as well as in prepared foods (nutraceuticals) or   biological insecticides.

In order to elaborate these products, it is necessary to obtain the natural additive extract concentrate required in each case. These are usually natural botanical extracts from plants, flowers, fruits, fungi, roots, etc.

For such purpose, it is required to carry out a process of separation and concentration of substances in liquid and solid mixtures, so as to obtain the additive concentrate that can later  be incorporated into the production process.

Vacuum concentration by means of vacuum evaporators is the most effective method nowadays to ensure  a high quality fruit concentrate.

This innovative procedure allows single-stage simultaneous separation and concentration processes. On the one hand, the solvent or  extractant is evaporated and, on the other,  the active principle is concentrated to dryness.

The whole process of separation and concentration takes place at low temperatures of  between 25°C and 30ºC, and therefore the additive active ingredients are not altered nor denatured.

In addition, vacuum concentrators are highly cost-effective and environmentally efficient, since they enable the recovery of solvents used in the process for later reuse and emit no fumes and emissions into the environment,  consuming a moderate amount of electricity (between 150 and 250 w/evaporated liter). They also can work autonomously 24 hours/day, requiring virtually no maintenance, with a life span of  over 20 years.

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Chemical, Food industry, Pharmacy & cosmetics aloe vera, natural ingredients, true aloe, vacuum concentration, vacuum evaporation, vacuum evaporators

Water and wastewater treatment

CSP pants consume a large amount of water, which is usually drawn from rivers and wells to generate vapor. The vapor is generated by turbines which require ultra-pure water in order for them to generate high quality vapor. For this reason, the incoming water to the power plant  needs to be treated at a water treatment plant (WTP) before use.

As a general rule, such treatment plant applies a reverse osmosis pre-treatment followed by a post-treatment by means of resins or continuous electrodeionization (CEDI)  treatment.

Once ultra-pure water is obtained, it is sent, by and large, to the steam generator turbine, a small amount of which is set aside to clean solar panels.

On the other hand, the generated effluents containing water treatment plant rejects (soil and sand, bacteria and different types of salt) will have to be treated at a wastewatert treatment plant (WWTP) to make them appropriate for discharge.

Wastewater is treated at WWTP’s by means of different technologies for salt crystallization.  The processes used to treat wastewater are mainly  chemical pre-treatment, membranes, vacuum evaporation and crystallization.

Air emissions treatment

The heat captured by solar collectors used in solar thermal power plants is pumped to the power block by means of an organic heat transfer fluid,  which contains  benzene-derived molecules. This fluid undergoes degradation, which poses a considerable security risk, since some of the degradation by-products are potentially hazardous.

Typical heat transfer fluid degradation mechanisms are contamination from water pipe residues and water from the water-vapor cycle; oxidation caused by the reaction of oil with oxygen in the air; and cracking that occurs inside absorber tubes and the auxiliary boiler, when the  heat transfer fluid reaches very high peak temperatures.

Three  are the products resulting from degradation:

1. Solid wastes, mainly carboxylic acids, carbon and carbon deposits, which are highly flammable and corrosive, due to their acidic properties.

2. Short-chain hydrocarbons produced by the breaking apart of bybiphenyl and diphenyl ether molecules.  This type of hydrocarbons have a very low boiling point and alter the viscosity and flash point.

3. Long-chain hydrocarbons produced by several short-chain residues joining together. This type of hydrocarbons have a very low boiling point and alter the viscosity and thermal properties.

In order to remove them, solar thermal power plants  are equipped with three technologies:  the primary filter and the reclamation and ullage systems.

It can therefore be noted at this point that  vapors vented from the ullage system contain benzene, which must be removed,  as it is carcinogenic and its emissions limits are very  strict.

The most appropriate technology for benzene emissions reduction is the use of activated carbon filters, since they contain inert material, which helps to retain volatile organic compounds and  return purified air.

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Power generation air emissions treatment, crystallization, CSP plants, effluent treatment process, electrodeionization, ETP, raw water, reverse osmosis, vacuum evaporation, Water treatment process, WTP