We've all heard of sewage treatment, but have you ever wondered where the sludge that is a by-product of sewage treatment ends up going? How to deal with them? Can they turn waste into treasure, and even promote the industrial level of related industries?

In fact, sludge treatment and disposal is a serious but often overlooked problem. China's annual sludge production reaches tens of millions of tons, of which only 20% to 30% have been stabilized and treated harmlessly.

If the sludge is piled up at will, it is likely to cause serious secondary pollution.

The mainstream sludge treatment and disposal technology in the world is anaerobic digestion technology.

This technology uses anaerobic microorganisms to decompose macromolecular organic matter in sludge into simple compounds such as methane, carbon dioxide, and water, and the resulting biogas can be used as a green fuel.

Anaerobic digestion technology not only solves the problem of sludge pollution but also realizes the recovery of biomass energy by the way, which can be said to kill two birds with one stone.

Some people may ask: Does sludge have the potential to turn waste into treasure? Although sludge is dirty and smelly, it is a "potential stock", and as long as it is used properly, it can generate energy and benefits.

In the 1980s, Canadian researchers did an interesting experiment: They built a factory and tried to use sludge to produce fuel.

They first removed most of the water and sediment from the sludge by mechanical means, and then put the dried sludge into a high-temperature still, and found that: the gaseous components obtained after distillation are converted into fuel oil, and the solid components are converted into charcoal.

As a result, the factory began to use this method to produce fuel, and each ton of sludge can produce 2 barrels of fuel oil and 0.5 tons of sintered carbon.

This example shows that sludge does contain components that can be used for resource utilization. Since then, with a further understanding of the composition of urban sludge, people have gradually realized that the sludge is rich in carbon, nitrogen, phosphorus, and other resource substances, which make the sludge the possibility of turning waste into treasure.

Nowadays, scientists from many countries in the world have made a lot of research results on the resource utilization of urban sludge and developed many ways of utilizing urban sludge.

For example, the carbon-containing components in the sludge can be used as a supplementary carbon source for the dephosphorization and deamination of sewage, methane or hydrogen can be produced, microbial fuel cells can be produced, or biodiesel can be produced.

Nitrogen-containing components and phosphorus-containing components can be used to make nitrogen and phosphate fertilizers, respectively.

Since it contains a variety of organics and metals, sludge can also be transformed into materials to prepare adsorption materials, catalytic materials, or energy storage materials.

Although sludge has a high utilization value, it is not easy to turn sludge into resources.

The treatment and disposal of sludge should be done step by step. First of all, it must undergo reduction and stabilization treatment, that is, reduce the mass and volume of the sludge, and degrade the perishable organic substances in the sludge.

Then carry out harmless treatment, so that it will not cause secondary pollution to the environment and will not endanger human health. The last is resource treatment, that is, the recycling of materials and resources with use value.

Each process has its sludge treatment and disposal technology.

For example, concentration and dehydration are suitable for reduction treatment, anaerobic digestion, aerobic composting and incineration are suitable for stabilization treatment, anaerobic biogas recovery, incineration heat recovery, land organic matter utilization, building materials inorganic matter utilization and other technologies can be used for resource treatment, and so on.

Of course, some of these techniques can satisfy multiple processing goals at the same time.

There are so many technical routes for sludge treatment and disposal, it seems that "all roads lead to Rome".

However, considering the maturity of the technology, the economic cost, the feasibility of sustainable development, and other factors, anaerobic digestion technology is still one of the most noteworthy technologies.