Manure management, slurry treatment and digestate valorisation in farms

Condorchem Envitech offers a complete solution for the treatment and monetization of wastewater and digestate in all types of livestock farms.

Our system offers numerous environmental and economic benefits:

• We provide a solution to an environmental problem by transforming a waste product that is otherwise difficult and expensive to treat into a source of self-sufficiency and revenue for farms.
• The self-supply of energy and fertilizers coming from the excrements allows your business to eliminate or reduce the costs of energy consumption, fertilizers, and waste management.
• Your farm will produce ecologically friendly and high-quality fertilizers that can be sold if you have a surplus. Revenue can be also generated from the sale of surplus energy.

Livestock farms, dairy farms and poultry farms produce a huge amount of wastewater which contains a high volume of organic waste coming from animal slurry and fertilizers.

We design and build manure management plants that transform the liquid waste into reusable resources and by products, such as:

• Clean and reusable water.
• Fertilizers.
• Biogas that can be used to generate thermal energy.

The following diagram shows the main processes and technologies involved in a plant designed to turn the waste generated in farms into valuable resources and by products.

1. Digestate treatment. The waste products (liquid sludge (*) + animal manure) is sent to the raw materials tanks for storage and mixing.

2. Anaerobic digestion of manure. The waste mixture is sent to the anaerobic biological digesters for treatment, resulting in the extraction of biogas and a digestate, from which a liquid fraction is separated (88%) and a solid one (2%).

3. Biogas production and treatment in farms. The biogas is sent to the co-generation plant to be converted into electricity and heat. Alternatively, biomethane can be produced by purifying the biogas.

4. Concentration and fertilizer production. The liquid fraction of the digestate, which contains valuable organic nutrients and minerals, undergoes several concentration phases by means of mechanical and thermal systems, thanks to which a concentrated liquid fertilizer is obtained which can be sold as well as clean water that can be discharged or re-used.

CASE #1: PRODUCTION FIGURES		CASE #1:ECONOMIC BALANCE SHEET
DESCRIPTION	VALUE	DESCRIPTION	VALUE
Volume of waste water treated (m3/yr)	2,200	Value of electricity generated (USD/yr)	437,400
Volume of primary sludge generated (m3/yr)	29,200	Value of calorific energy (USD/yr)	257,760
Volume of chicken manure (Tn/yr)	15,000	Value of fertilizers (USD/yr)(Tn/yr)	532,280
Biogas production from sludge (m3/Tn)	50	Savings in sludge management(USD/yr)(m3/Tn)	187,500
Biogas production from manure (m3/Tn)	70	Total income (USD/yr)	1,414,940
Volume of biogas from sludge (m3/yr)	1,460,000	Operating Expenses (USD/yr)	329,481
Volume of biogas from manure (m3/yr)	1,125,000	Economic return (USD/yr)	1,085,459
Total volume biogas (m3/yr)	2,585,000	Project investment (USD)	4,200,000
Volume of methane (m3/yr)	1,581,000	Period to break-even point (years)	3.9
Electricity generated (KWh/yr)	4,374,000
Calorific energy production (KWh/yr)	6,444,000
Fertilizer production (Tn/yr)	3,550 (*)

CASE #2: PRODUCTION FIGURES		CASE #2: ECONOMIC BALANCE SHEET
DESCRIPTION	VALUE	DESCRIPTION	VALUE
Volume of dilution water (m3/yr)	43,800	Value of electricity generated (USD/yr)	1,288,369
Volume of chicken manure (Tn/yr)	74,825	Value of calorific energy (USD/yr)	498,490
Biogas production from manure (m3/Tn)	73	Value of fertilizers (USD/yr)	2,353,500
Volume of biogas from manure (m3/yr)	5,479,613	Total income (USD/yr)	4,140,359
Volume of methane (m3/yr)	3,013,788	Operating Expenses (USD/yr)	740,000
Electricity generated (KWh/yr)	12,883,695	Economic return (USD/yr)	3,400,359
Calorific energy production (KWh/yr)	12,462,266	Project investment (USD)	7,800,000
Fertilizer production (Tn/yr)	15,690 (*)	Period to break-even point (years)	2.3

Depending on the chemical composition of the by-products, the processes necessary for their conversion into fertilizers varies. The by-products we have worked with mostly for recovery as fertilizers are the sludge from aerobic purification processes and the digestate produced in biomethanization plants.

To recover phosphorus in the form of a solid fertilizer, it can be crystallized in the form of struvite, a slow-release mineral fertilizer composed of magnesium, phosphorus and nitrogen, with a low metal content. This slowly provides nutrients to the soil, favoring its absorption by plants and reducing surface losses that can end up in water bodies.

In addition, the production of liquid fertilizers rich in ammonium can be viable through an adsorption-desorption process with zeolites and membrane contactors.

Sometimes, to achieve a specific relationship between the main nutrients, surplus nitrogen needs to be removed. This can be done via a process under microaerophilic conditions with low energy consumption.

Another way of transforming waste into fertilizers is, firstly, to mix the waste with other organic waste and other mineral fertilizers to adjust the nutrient levels (N/P/K) to commercial values. Secondly, the resulting mixture undergoes vacuum evaporation to remove the water and transform the material into a stable and easy-to-use solid.

In all cases we work with the customer to evaluate the identified source of waste to determine the potential of the fertilizer. Samples can be sent to our laboratory for a complete analytical evaluation; after which, our technical team will work with the customer to establish a profitable program to obtain the maximum potential of the fertilizer produced.

Fertilization is an irreplaceable agrarian practice whose main objective is to maintain soil fertility, and is not limited to restoring that extracted by the crop, but also those components lost by the soil due to washing, degradation and erosion.

NPK complex fertilizers are products that contain two or three primary nutrients (N, P, K) and possibly secondary nutrients (Ca, Mg, S) and micronutrients (e.g. Zn, Cu or B). They are applied to balance the soil content in nutrients according to their content, the needs of the crop to be planted and the expected yield. They can be solids (granular form) or liquid, with the latter being increasingly common.

However, the amount of fertilizers consumed annually is very high (over 200 million tons in 2018 according to the FAO) and increasing in recent years. This leads to a huge amount of waste, much of which has significant nutrient content (N/P/K), being produced and accumulating in landfill sites.

Thus, the circular economy in the production of fertilizers needs to be improved. This circular process is based on the recycling of products, optimizing the use of mineral resources, recovering and incorporating the by-products produced, minimizing emissions and reducing dependence on non-renewable energy sources.

In energy recovery, the waste is mainly used as fuel or in some other way to produce energy.

Energy recovery processes drastically reduce the volume of waste while producing usually electrical or thermal energy. Energy is often consumed in the process itself, such that waste management finds farther savings in the purchase of electricity.

There are different waste treatments by which the energy can be recovered. The most appropriate treatment depends on the type of waste and its chemical composition.

Processes and technologies

The main processes used by Condorchem Envitech are the following:

Biomethanization

Biomethanization is a biological, multi-stage process in the absence of oxygen, which transforms the most degradable fraction of organic matter into biogas. This is performed by a heterogeneous population of microorganisms forming a mixture of gases, consisting mainly of methane and carbon dioxide, with other gases in a smaller proportion (e.g. water vapor, CO, N₂, H₂, H₂S, etc.).

Biogas is a source of energy because it is a combustible gas with a high heat capacity (5,750 kcal/m³), whose energy is used in cogeneration engines, boilers and turbines (generating electricity, heat or as a biofuel).

The type of material to be digested greatly influences the yield and composition of the biogas obtained. For maximum production, it is best to use waste rich in fats, proteins or carbohydrates, as their degradation entails the formation of significant amounts of volatile fatty acids, precursors of methane.

Biomethanization is an appropriate process for the treatment and recovery of agricultural, livestock and urban waste, as well as for the stabilization of sludge from urban wastewater treatment.

Pyrolysis

Pyrolysis is the thermal degradation of a material in the absence of added oxygen, so decomposition occurs by heat, without combustion reactions. The basic details of this process are shown below.

• The only oxygen present is that in the waste to be treated.
• Working temperatures are between 300°C and 800°C.
• As the most volatile compounds do not oxidise, the calorific value of the synthesis gas from the pyrolysis process ranges from 10-20 MJ/Nm³.

As a result of the process, the following is obtained:

• Synthesis gas (whose basic components are CO, CO2, H2, CH4) and more volatile compounds from the cracking of organic molecules, together with those already existing in the waste.
• Liquid waste, basically composed of long chain hydrocarbons such as tars, oils, phenols or waxes, formed by condensing at room temperature.
• Solid residue, composed of all non-combustible materials, which have either not been transformed or which form as a result of a molecular condensation, along with a high content of coal, heavy metals and other inert components already in the waste.

Low working temperatures cause less volatilization of carbon and other precursor pollutants in the gas stream, such as heavy metals or dioxins. Therefore, combustion gases will theoretically require less treatment to meet the minimum emission limits established in the Incineration Directive. Compounds that do not volatilize will remain in the pyrolysis residues and will need to be properly managed.

To treat waste by pyrolysis, a series of requirements must be met. However, it is difficult to establish the type of waste considered adequate or inadequate, since it is closely related to the type of reactor used and the operating conditions. Basically, the waste considered most suitable is paper, cardboard, wood chips, garden waste and selected plastics. Whereas, bulky waste, metals, construction materials, hazardous waste, glass and plastics such as PVC are not acceptable.

Gasification

Gasification is a partial oxidation process of matter in the presence of quantities of oxygen lower than those required stoichiometrically. In general terms, the details for the gasification process of a waste stream are the following:

• Air, oxygen or steam is used as a source of oxygen, and sometimes as a carrier to remove reaction products.
• Working temperatures are typically over 750°C.
• The chemical reactions produced in this process are of two types: molecular cracking – the temperature causes the weaker molecular bonds to break into smaller molecules which are usually volatile hydrocarbons – and gas reforming. These gasification reactions are process specific and the water vapor in them usually intervenes as a reagent.

As a result of the gasification process, the following is obtained:

• Synthesis gas, composed mainly of CO, H2, CO2 and N2 if air is used as a gasifier, and CH4 in a smaller proportion. Tars, halogenated compounds and particles as secondary products.
• Solid residue of non-combustible and inert materials present in the waste, which usually contains part of the ungasified carbon. The properties of this residue are similar to slag from incineration plant furnaces.
• The amount, composition and calorific value of gases from gasification depend on the waste composition and the temperature and volume of air and steam used.

Synthesis gas from the gasification process potentially has several uses:

• As a raw material in the production of organic compounds, such as the direct synthesis of methanol, ammonia, or for its transformation into hydrogen by steam or catalytic reforming.
• As a fuel in electricity production by thermal cycles other than those of water vapor, whether combined or simple cycles, in gas turbines or internal combustion engines.
• As fuel in traditional boilers or ovens.

However, not all waste is appropriate for gasification; it can be used to treat only specific materials. The material fed must be ensured to have the following properties: the minimum content of inert or wet components; a particle size of 80-300 mm; a sufficient amount of carbon to be able to carry out the gasification process reactions, without dangerous substances; and, if possible, a high calorific value.

Incineration

During incineration, combustion takes place, which is a chemical reaction based on total thermal oxidation in excess of oxygen. The general requirements for waste incineration are the following:

• Oxygen in excess, with respect to the stoichiometric reaction, during combustion to ensure complete oxidation.
• The combustion temperature is typically between 850°C and 1,100°C after the last secondary air injection, depending on the halogenated compound composition of the residue to be treated.

As a result of the incineration process, the following is obtained:

• Combustion gases, composed mainly of CO2, H2O, unreacted O2 and N2 from the combustion gas air supply, as well as other compounds in smaller proportions from the different waste components. The components present in lesser quantities will depend on the composition of the waste to be treated. For example, they may contain acid gases from reactions with halogens, sulfur, volatile metals or organic compounds that have not oxidized. Finally, the combustion gases will contain particles, which are carried by the gases.
• Solid waste, mainly composed of inert slag, ash and waste from the combustion gas purification system.

The overall process converts practically all the chemical energy contained in the fuel into thermal energy, leaving some chemical energy not converted in the combustion gas and a very small part of the chemical energy not converted in the ash. The heat from this process is used to produce superheated steam, with thermal yields of the order of 80%, due to the heat losses in both the furnace and the boiler and the minimum temperature required for the combustion gas exit from the recovery boiler.

The incineration processes are very flexible in terms of heterogeneous fuels, so they can treat urban rubbish (MSW), industrial waste, hazardous waste, sewage sludge and hospital waste.

Plasma production

Plasma is a state of matter, consisting of a gas subjected to high temperatures in which virtually all the atoms have been ionized. The result is a fluid formed by a mixture of electrons, ions and free neutral particles, being as a whole electrically neutral, but conducting electricity.

The description of this process is as follows:

• Plasma is produced by passing an inert gas through an electric field between two electrodes, forming the so-called plasma arc.
• Working temperatures vary between 5,000-15,000°C.
• The following reactions occur within the gas: dissociation of atoms, loss of electrons from the outer layers and formation of positively charged particles.
• The rationale for the process is as follows: if a gas in the above conditions is introduced into an electric field, an electric current will be produced, as a result of the free electrons going to the positive pole of the electric field, and the positive particles to the negative. This electrical current determines a resistivity and, therefore, a transformation into heat that depends on the electrical intensity. Thus, increasing the intensity of the electric field increases the electronic and cationic intensity, the transformation into heat and the temperature of the gas.
• A practical limit to this process is the mechanical and thermal strength of the electrodes.

As a thermal method for waste treatment, plasma has 3 possibilities:

• Treating hazardous gas, whose molecular structure is destroyed by subjection to the working temperatures. Clear examples are the destruction of PCBs, dioxins, furans and pesticides.
• Vitrification of hazardous waste, for both organic waste – whose molecular structure is destroyed – and inorganic, by fusing it into a vitreous mass. After cooling and solidifying the melt, the waste is physically captured within the vitreous mass, becoming an inert solid and minimizing the possibility of leaching.
• Plasma gasification, in which the thermal energy contained in the plasma itself is used as a source of heat from the (normally electrical) energy consumed for its production. Thus, the final products are: a gas, consisting mainly of carbon monoxide and hydrogen, and a solid residue, consisting of an inert, generally vitrified slag.

As a result of the tests carried out in the pilot plant, this technology could treat a wide variety of waste, such as MSW, industrial waste, biomass, sanitary waste, vehicle scrapping, tires, plastics and special waste.