|M.Sc Student||Inna Litinetsky|
|Subject||The Impact of Several Chemical and Physical Factors on|
Struvite Sediment Strength under Laboratory
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Armon Robert|
|Full Thesis text|
Struvite deposits can be found in almost every municipal wastewater treatment plant that operates anaerobic digesters. There are severe problems caused by high levels of phosphate in waste water and spontaneous struvite precipitation.
Currently in the industry the actions taken against the negative effects of struvite precipitation centralize around the “struggle with the consequences” - by causing intentional struvite precipitation in designated devices installed in waste water treatment facilities. However it does not solve the problem entirely.
A more effective way would be a “struggle with the sources” - preventing the formation of the struvite layer. To accomplish that, the factors causing the formation of a hard struvite layer need to be found. This research centralizes around an investigation of various factors that could influence the precipitation process.
The goal of this research was to achieve at laboratory scale formation of a hard struvite layer like the one formed on pipes and equipment of wastewater treatment plants.
In this research two different directions were taken - chemical precipitation (in presence of inorganic material, organic material and bacteria) and electro-precipitation.
Struvite precipitation in laboratory resulted in powdery or flakey struvite sediments. The exceptions were struvite precipitation in presence of calcium, and at increased temperature (60°C and higher), the combination of temperature (>60ºC) with the presence of dissolved calcium (from addition of CaCl2) gave the strongest effect. Harder clumps of struvite formed, however a hard struvite layer was not achieved.
These results cannot fully explain the formation of a hard layer of struvite in the wastewater treatment plants that are located in different climatic conditions, from north Europe (in cold climatic conditions) to south California (in hot climatic conditions). However, this could explain the accelerated formation of such a layer in hot climatic conditions.
In the wastewater treatment plant the formation of a hard layer may take several years (the fastest formation described in literature was after 6 months at the Sacramento Regional Wastewater Treatment Plant in California, and is regarded as an unusual case), such time frames were not replicated in this research.
In the electro-precipitation process among all cathodic materials tested (carbon steel, copper, aluminum, stainless steel and titanium), the most even and homogenous layer of struvite coating was achieved on stainless steel. However, the formed struvite layer was fickle (could be easily scraped off). None of the tested additions or coatings improved the adhesion of the struvite layer onto cathode surface.