Good day everyone. Glad to be back here again after being away for a very long time. Today, I will be considering a nutrient recovery using a waste material: Periwinkle shell.

Image by author

My first contact with periwinkle shell dates back to my days as a little boy in a riverine community, my playmates and I would go out and pick the stuff from around our surrounding and have a sumptuous meal thereafter. Once done with the meat, we discarded the shell as a waste. A heap of the discarded shell was an eyesore in our community. We knew nothing about the uses of the shell.

Years later, some guys from the southeastern part of our country came to purchase these "waste" and how glad our people were to sell them off cheaply. We never cared to know what these guys do with the "waste". We were too glad to exchange our waste for wealth.

Fast forward ten or more years later, I was contemplating ways of recovering phosphate from wastewater, and I remembered "my childhood play food": Periwinkle shell.

Phosphate as an essential nutrient

Phosphorus and nitrogen are nutrients that are crucial to intensive agriculture and vital for food security. While there is an abundance of nitrogen in nature, phosphorus is not so fortunate. In other words, it is a non-renewable resources. Phosphorus is sourced mainly from phosphate rock which is not evenly distributed globally. Some researchers have predicted that we could run out of phosphorus in the next 50 to 70 years.

Phosphorite or phosphate rock

Meanwhile, wastewater from human sewage and local industries such as abattoir, piggery, tannery and so on are rich in phosphate and nitrates. These nutrients laden wastewater are discharged indiscriminately into the environment especially in climes where there is no regulation or poor implementation of policies put in place to checkmate such unwholesome act.

Eutrophication

Wastewater rich in phosphates and nitrates facilitate uncontrollable algae and macrophyte bloom leading to eutrophication. Eutrophication makes a mess of water bodies affecting aquatic organisms negatively. While eutrophication of lake is a natural phenomenon, discharge of nutrient rich wastewater into water bodies greatly accelerate the process.

Eutrophic pond

So, there are essentially two compelling reasons to recover phosphate from water bodies viz:
The fact that phosphorus which takes the form of phosphates in solution is a scare but essential nutrient for agriculture and the need to improve the quality of water for reuse and ensure a safe environment.

Technologies for nutrient recovery

There are numerous technologies that have been deployed in the recovery of nutrients, particularly, phosphate from wastewater. They can be broadly classified into physical, chemical, biological and combinatory technologies.
Of all the technologies, adsorption stand out basically because of the ease of operation and cost.

Adsorption

In simple terminology, adsorption is a process that occurs when a gas or liquid solute (adsorbate) accumulate on the surface of a solid (adsorbent), forming a film of molecules or atoms. Adsorption is different from absorption. While the former is a essentially a surface phenomenon, the latter is a bulk phenomenon that occur when a substance diffuses into a liquid or solid to form a solution. The term sorption is used to described the two processes while desorption is the reverse process.

Both organic and inorganic materials have been utilized in the adsorption of nutrients from wastewater. In recent times, researchers have focused on utilization of waste materials such as crab shell, fly ash, eggshell and so on. This is one way to ensure waste minimization and recycling.

At the point of conceptualization of my research, it was natural for me to recollect periwinkle shell as a waste material that can be used for phosphate adsorption from wastewater, having established from literature that its usage has not been reported.

The experimental design was simple. Pulverized periwinkle shell of known size was divided into four and labelled as sample A, B, C and D. Sample A consisted of only the pulverized periwinkle shell, B and C were calcinated at 400 and 750 degree Celsius while D was modified with MgO and calcinated at 800 degree Celsius. All the samples were subjected to phosphate adsorption from wastewater.

(Image of sample A and calcinated variety by author)

The research questions were simple. Does surface modification affect the adsorption capacity of periwinkle shell? If yes, how?

From the result of the experimental set up, it was deduced that surface modification thus affect the adsorption capacity of periwinkle shell. The question regarding how was also answered from the result obtained from various characterization performed on the samples.

Basically, the result revealed that calcination transform the major component of the shell which is calcium carbonate to calcium oxide which has a greater affinity for phosphate. This result is corroborated by the work of other researchers.

This research is still ongoing but at least I have been able to discover for myself an important use of what we thought was a useless material as a child.

Thank you for stopping by to read my post. Bye, for now.

Reference

Source of image on phosphorite

Source of image on Eutrophic pond

Assessing the suitability of solid aggregates for nutrient recovery from aqua systems

Adsorption of phosphate from aqueous solutions using calcined waste eggshell

Technologies to Recover Nutrients from Waste Streams: A Critical Review https://doi.org/10.1080/10643389.2013.866621