Low-Temperature Conversion — an alternative way to dispose of sewage sludge

Due to the increased rate of urbanization and industrialization, the world is seeing a significant increase in waste generation. At this time, proper waste management is required otherwise it can have huge environmental impacts and cause serious problems.

The main goal in waste management is to reduce waste or recycle it for some other productive uses. However, this cannot be the final solution as some of the waste products need to be treated, stored, or disposed of due to their hazardous nature. Such wastes are treated by several chemical, thermal, biological, and physical methods to eliminate the harmful elements. Low-Temperature Conversion is observed to be an efficient and friendly method to dispose of byproducts of wastewater treatment i.e biosolids.

What is sewage sludge?

Sewage Sludge, commonly known as “biosolids” is a semisolid residue recently introduced by the wastewater treatment industry. Sewage sludge is often misinterpreted and mixed with biosolids as biosolids can be obtained from sewage sludge. Biosolids are defined as the product obtained when sewage sludge undergoes treatment for stabilization and pathogen reduction to eliminate all the toxic chemicals to be applied to land in the form of fertilizers. Among several others, sewage sludge is the mud-like hazardous byproduct produced after the municipal wastewater treatment process.

Sewage sludge contains both organic and inorganic materials, pathogens, and varying concentrations of several trace elements and plant nutrients. The varying compositions of sludge are because the wastewater treated in the industries comes from different sources like urban towns, industries, and medical facilities. It also depends on the treatment process the wastewater goes through.

There are several types of sewage sludge produced from different wastewater treatment processes and with different compositions.

• Primary sludge is the type of sewage sludge generally produced after the processes of sedimentation, chemical precipitation, or other primary treatment methods.
• Secondary sludge is referred to as biomass that is produced as a result of biochemical processes. When primary sludge undergoes further industrial processes, it turns into secondary sludge.
• Mixed Sludge is also known as thickened sludge, produced when secondary sludge is further treated to stabilize and reduce the overall volume.
• Digested sludge can be both primary and secondary sludge produced after the stabilization by anaerobic fermentation.
• Tertiary Sludge is produced when the base sludge undergoes further wastewater treatment by adding a flocculation agent.

What are the most common ways of disposing of sewage sludge?

As explained above, the type of sludge primarily depends on the composition of wastewater and the process used for its treatment. The techniques used for wastewater treatment results in sewage sludge of varying formations.

According to 40 CFR (Code of Federal Regulations) Part 261, Sewage sludge is determined to be a hazardous waste, so it becomes important to manage and dispose of the waste carefully so that it does not affect the environment.

There are 3 most common ways to dispose of sewage sludge.

• Landspreading
• Incineration
• Landfilling

However, before applying sludge to the land, it needs to be treated to eliminate any toxic chemicals and foul odor from it.

Some of the sludge treatment processes are mentioned below.

• Conditioning
• Thickening
• Dewatering
• Stabilisation or Disinfection
• Thermal Drying

Landspreading

One of the most common ways for reusing the agricultural nutrients present in sewage sludge is by applying them on land. Every type of sludge including liquid, semi-liquid, solid, or dried can be applied on the land given that they are treated well to eradicate toxic chemicals which could possibly damage the fertile land. Several factors influence landspreading like land quality, geographical locations, and culture types.

Sewage sludge tested under Sludge Regulations can only be used for landspreading.

Incineration

Incineration is another commonly used method for disposing of sewage sludge. It is a thermal process that mainly depends on the type of sludge to oxidize organic matter contained in the sludge and to stabilize it.

Different incineration processes can be considered for sludge and are mentioned below.

• Mono-incineration process involves the treatment of specific sludges in dedicated incineration plants
• Incineration of sludges with other household wastes
• Co-incineration is a thermal oxidation process in which sludge is used as a fuel in plants. The main purpose of this process is to generate energy from sludge or other production materials for coal and cement plants.

Landfilling

One of the major routes for sludge disposal is landfilling. Landfilling becomes a useful solution when there is no other way to dispose of sludge. It involves mixing the concentrated sludge with other solid waste in municipal landfills.

Commonly, there are two ways for sludge landfilling.

• Mono-deposits is a method of landfilling in which sludge is disposed of in a dedicated land.
• Mixed-deposits landfilling includes sludge and municipal wastes as well.

However, the regulations of landfilling for disposal of sludge are set out to be different in every country and do not satisfy the future goals for the environment. In 2003, European legislation regarding landfilling stated that “Member States shall set up a national strategy for the implementation of the reduction of biodegradable waste going to landfills”.

Why is this such a problem?

Sewage sludge is hazardous according to CFR and it is important to handle such wastes carefully.

Reducing the overall volume of sludge and then stabilizing the organic compounds present in it are the two main goals before the final disposal of the sludge. It is because tested sludge does not have any bad odor and can be handled or disposed of without causing any environmental impacts. Landspreading or landfilling are not considered a permanent solution as they can damage the land or occupy vast areas making them inhabitable and reducing fertility. As a result, there is a need for better treatment and disposal techniques that could greatly reduce the sludge volume or use it more productively.

Increased Production of Sewage Sludge

According to a report, approx. 1.5 Mt of sewage sludge is produced in the United Kingdom annually. (A. Nuamah, E. Lester, in Comprehensive Renewable Energy, 2012)

In several countries, sewage sludge is considered a cultural bioresource as it contains a significant amount of plant nutrients and some non-toxic organic materials. On the other hand, it does also contain toxic organic matter, heavy metals, pathogens, viruses, and bacteria. It is important to handle raw sewage sludge greatly as it may cause severe impacts on environmental sustainability by polluting water, lands, and air.

Sewage sludge also contains inorganic nitrogen and after applying to land it goes through several physical and biochemical processes that could form NO2 which can ultimately cause chemical smog, ozone layer depletion, and other forms of acid rain. Sewage sludge when dumped into the water could cause harm to water bodies and give rise to one of the most common environmental pollutions, eutrophication. The heavy metals present in sludge could damage plants or somehow enter the human body could result in serious health problems. Pathogens are found in abundance in sludge that could pollute the atmosphere and water to a great extent.

All these challenges require urgent and efficient solutions for the safe treatment and disposal of sewage sludge.

Currently, there isn’t any single solution or technology available that can eliminate sewage sludge completely from the environment. (Miksch and Sikora, 2018; Bień et al., 2011).

Regulation of Land-applied Sludge

There are now strict rules towards landfilling and landspreading because of several environmental and public health risks. These practices are now becoming unpopular due to increased challenges associated with them. At the same time, the incineration thermal process produces toxic gases released in the atmosphere that cause serious air pollution despite the fact that the process can reduce sewage sludge mass from 95% to 96% (source). In addition, incineration is also considered an expensive solution for the treatment of sludge as dewatering and drying are involved in it.

Landspreading in the form of land farming is also disregarded because of dangers linked to heavy metals and pathogens present in sewage sludge. Moreover, it could hurt the land quality for farming and bring other potential risks with it.

Why is a Low-Temperature Conversion solution for the disposal of sewage sludge?

Low-Temperature Conversion (LTC) is a pyrolytic thermochemical decomposition process currently gaining popularity given its several benefits over traditional disposal methods for sewage sludge. At this time, LTC is an alternative technology that could make waste materials including sludge, reusable.

The LTC process reduces the organic matter from the sewage sludge and other waste pollution of the Earth and promises to produce clean energy in return in the form of White Hydrogen. The sewage sludge in the LTC process is recycled into conversion gas by the thermochemical process that is then turned into useful products such as Hydrogen, synthetic fuels, electricity, or harmless useful chemicals.

As a result of Low-Temperature Conversion, no toxic gases arise. Inorganic materials are also eliminated without generating any pollutants. Unlike landfill and incineration, LTC ensures environmental sustainability, energy recovery, and converts waste materials into more environmentally friendly products.

WHC- a new game-changer coalition

The White Hydrogen Coalition is an international association that is promoting the use and production of clean energy through various technologies.

The main aim of this revolutionary coalition is to speed up and facilitate the adoption of the LTC technology.

Implementing blockchain technology, WH2C believes in a transparent and greener environment. They offer amazing opportunities for those who participate or support their motive of a better and cleaner future. In return, the supporters will be given White H2 Coin (WH2C) to participate in the coalition. WHC is a team of motivated tech supporters who support disruptive technologies that can transform waste materials like sewage sludge into environmentally friendly clean energy mainly in the form of White Hydrogen.

What are the positive externalities of Low-Temperature Conversion?

LTC technology for the disposal of sewage sludge has the potential in helping to achieve future climate and green energy goals. Despite its great benefits, LTC is still not widespread, but it will mature more as a technology in the near future.

With the expansion of the world’s population and increasing urbanization, the quantity of sewage sludge production is also increasing giving rise to even more serious challenges. The traditional disposal methods like landspreading and landfilling are no longer acceptable and are under strict regulatory rules. This is the reason why the world needs more eco-friendly and efficient technologies to handle sewage sludge properly.

Currently, thermochemical processes like LTC are considered more beneficial methods in sludge management due to their several benefits like mass reduction, destruction of pathogens, and clean energy production. Instead of wasting or disposing of sludge, reusing and recovering energy from it through LTC or other thermochemical processes is more favorable for the environment as well as industries. This solution can help in maintaining economic feasibility and environmental sustainability. LTC and other emerging technologies are more beneficial methods for sewage sludge disposal that could reduce volume and produce energy or other resources from it, including promising elimination of pathogens.

One of the main benefits of LTC is by producing White Hydrogen and using it as a fuel could benefit industries and governments in replacing fossil fuels.