Talking about sewage, we have to be prepared to talk about dirty things. Well indeed we have to be prepared to talk about the waste that living beings produce, and it can be a really dirty if we discuss it environmentally.
Where do you think your sewage go? Most of it go into sewage treatment plant that will try to remove contaminants in it before it goes into water bodies like river, sea, or underground water. The problem is, not all efforts to remove contaminants can 100% purify it.
In this case, even though we have a good sewage treatment plant in our city, it doesn’t mean that we can directly drink the water it produces after processing our pee and poop. Wait, what? Yes, by entering water bodies, there is huge chance that we are reusing the water we got from sewage treatment plant.
Disgusting indeed, but that’s a fact that most of us we don’t know. Bu what if we use the power of plants to process it in a mutual symbiosis? Like using our sewage to fertilize them and we ‘harvest’ all the benefits we can get from them?
Here in this article we are going to talk about it.
Sewage Sludge As Fertilizer
Anytime we flush something from our sinks and toilets, it goes down into sewer. There are two endpoints to the sewer, which are sewage treatment plants or water bodies. In most countries it goes directly into water bodies because building sewage treatment plant requires too much money for them.
But wait, isn’t wastewater contain so much organic matters that might be useful for us? Indeed, it does. It can be used as fertilizer for that very reason. However, using wastewater as fertilizer is not as simple as spreading dried leaves on your lawn.
The wastewater we flush down from our sinks and toilets indeed contains so many nutrients and organic materials such as fat, carbohydrates, urea, and minerals. On the other hand, it also contains pollutants such as heavy metals, oils, chemicals, even disease-related microorganisms.
Applying it as fertilizer would make it a double-edged sword. On one hand the organic matters and nutrients in sewage will fertilize the soil as good or maybe even better than chemical fertilizers, which are already known as dangerous and harmful to the environment.
But on the other hand, we cannot deny that it still contains as many harmful materials in it. And if we insist on applying it as fertilizer, we would just add another harmful material to the soil. This is the case that experts are trying to work out
What Happens In The Plant?
Of course, what researchers are trying to figure out are not literally the sewage we produce daily. What we are talking about is the processed sewage as the result of treatment plant’s work. Many researchers are still debating whether it is environmentally correct to use treated sewage as fertilizer.
Before talking about that, let’s talk about what happens in sewage treatment plants. First thing first, the wastewater is collected into a big pond before being processed. It is meant to settle heavy solid waste into the bottom of the pond, and lighter waste including oil and grease will float at top.
Next, it is introduced into indigenous water-borne microorganisms to remove dissolved and suspended biological matter. In other words, it is ‘washed’ using microorganisms, and the final product is ‘cleaner’ version of the wastewater.
After all those things, the final steps are conducted. The purpose for the final steps is to further improve output quality before discharging it back into nature. It may include filtration, nutrient removal, disinfection, or all of those combined.
The end results are two kinds of products: first is sewage sludge, and the other is effluent. Both of them still contain nutrients derived from organic matters it contained, but with the treatments done the end products are far less dangerous to the environment. Yet, the words ‘far less dangerous’ mean it is still not completely safe.
Harvesting Phosphate From Sewage
So, what’s the required process to make both sewage sludge and effluent safe as fertilizer? For sewage sludge, harvesting its most beneficial compound only, which is phosphorous. Thanks to advanced technology discovered in the past decade, we can do that effectively.
One of the examples is Phosphorrecycling—vom Rezyklat zum intelligenten langzeitverfügbaren Düngemittel—PRil (phosphorous recycling—from recyclate to smart, persisting fertilizer). This is a joint-project of Fritzmeier Umwelttechnik GmbH & Co. KG, Fraunhofer Research Institution for Materials Recycling and Resource Strategies IWKS at Alzenau, and ICL Fertilizers Deutschland GmbH.
“The phosphorus we recover from the ash with this innovative process is 50 percent plant-available in a water-soluble phosphate fertilizer. In contrast, the phosphate in pure sewage sludge ash is all but unavailable to plants,” said Dr. Lars Zeggel, project manager at the Fraunhofer IWKS.
To do the work, the researchers are asking for help from particular bacteria that can produce sulfuric acid when being exposed to carbon dioxide. The end product is solid iron phosphate precipitates which then can be used for fertilizer.
Not only it produces eco-friendly phosphate, it also doesn’t require a lot energy to do the work because the researchers are using a technique called membrane filtration. “We have been able to adapt the membrane filtration so that we can now remove 98 percent of the sulfate from the water and ultimately circulate 75 percent of the process water,” said Zeggel.
Another method that we might be able to use to harvest something from sewage is by microwaving it. Yes, you don’t read anything wrong, because researchers from Civil & Environmental Engineering, FAMU-FSU College of Engineering have tried it out.
But the thing that the engineers were microwaving was not the waste itself, rather it was a byproduct of waste treatment process called biosolid. Biosolid is literally dead bacteria floating on top of processed wastewater after doing their job.
Most of the time, it ends up in landfill and pollute it with its heavy metal contents, which was gained from wastewater treatment process. Gang Chen, one of the researchers said that without being processed, the biosolid will be nothing good.
“If farmers apply the biosolids at this stage, these metals will separate from the biosolids and contaminate the crop for human consumption. But removing heavy metals isn’t easy because the chemical bonds between heavy metals and biosolids are very strong,” he said.
That’s why, it needs to be microwaved to separate the bonds between the two. The end result is an organic fertilizer that can be used to replace chemical fertilizers. “One lesson I would like to share with everyone: Be observant. For any problem, the solution may be just around you, in your home, your office, even in the appliances you are using,” said Chen.