Abstract
Decentralized wastewater treatment facilities have become more popular throughout the years as they service rural areas which lack the infrastructure to set up a centralized system. The aim of this project was to investigate the ongoing challenge of sludge dewatering in on-site de-sludging trucks, by testing an array of polymers in the field to be able to narrow down the list and further investigate performance through dose optimization. The approach taken in the project was to divide the work into two sections, first screening the twelve available polymers in the field by travelling to Seljord, Noway then conducting a manual pour test and recording the initial dose where flocculation is observed. Once the polymers have been tested a detailed analysis of the results is conducted to be able to narrow down the polymer list to polymers A,C,D and X. Following that the optimization phase commences where jar test's are conducted for each sample, this used nine liters per test and all four polymers were tested on the six available samples. The jar tests were conducted with a range of doses around the base dose observed in the field. To expand further, the stock solutions used all had a concentration of (0.1\%), the stirring speed was set up to resemble ideal mixing conditions.
Turbidity was a key factor in the determination of the optimum dose of each polymer, so after every jar test turbidity for each jar was measured. By doing so, the optimum dose was selected based on lowest turbidity alongside one of the remaining eight jars as the non-optimum dose to go through analytical and sludge testing, this was done to ensure a comparison between the optimum dose and non-optimum dose. The analytical tests were conducted on the water phase by using Hach cuvettes for chemical oxygen demand, total nitrogen, ammonium, nitrate, nitrite, total phosphorus and ortho-phosphate to better understand the water quality of the reject water. The sludge was tested using the capillary suction time test where the dewater-ability of the sludge was recorded, and the sludge volume index was used to better understand the flocc quality and settle-ability.
The results show that all four polymers were effective in improving the water quality of the reject water and improving dewater-ability of the sludge. Furthermore, a key aspect found was that the optimum dose for each polymer varied due to the average suspended solid content of the sample, for example polymer X's optimum dose for Biovac 1 was (4.5 mg/L) where it had an average suspended solid content of (14497.49 mg/L) compared to polymer D where the optimum dose was found to be (11 mg/L). Whilst the optimum dose for polymer X was (9 mg/L) for the sample Kingspan 4 which had an average suspended solid content of (11625 mg/L) compared to polymer D's optimum dose for Kingspan 4 was (7 mg/L). Moreover, Biovac 7 had the lowest suspended solid content of (800.1 mg/L), which made it very hard to see flocculation occur due to the low solid content present this caused the optimum dose of the polymers used to be amongst the highest, polymer C and D (12 mg/L) and polymer X (8 mg/L).
