Abstract
The need for clean water has become a critical issue with the rising demand due to expansion of population, as industrialization and urbanization has significantly contributed to the increase of pollutants in water. Contaminants ending up in the sewage negatively impact public health through facilitating the spread of disease and harming the surrounding environment. Therefore, it is crucial to effectively treat municipal wastewater in urban cities to tackle this problem.
This study aims to investigate dosage of flocculants and optimize the treatment efficiency of municipal wastewater in Trondheim, specifically focusing on the chemically enhanced treatment process employed at the Ladehammeren wastewater treatment plant. The goals of this research are achieved through a comprehensive series of experimental designs to identify most significant factors in the process and determining optimal settings to enhance efficiency, in addition to achieving at least 70% Suspended solids (SS) removal to ensure compliance with regulatory guidelines. The results of each design are then analyzed in the JMP pro 17 software through statistical and graphical techniques. Experimental methods included a Phipps and Bird programmable jar tester is utilized for implementing the design of experiment in the laboratory, it is set up to mimic the process at the Ladehammeren wastewater plant where the water sample first undergoes a fast mixing phase and then a gentle mixing phase followed by a sedimentation period. Responses in the designs were set as the results of a gravimetric analysis to determine the removal percentage of suspended solids and light transmission results from a turbiscan which provides quantitative data on the water's clarity. Additionally, pH and conductivity measurements are conducted to monitor the water samples.
Initially, a screening design of experiment involving seven factors was carried out, using the current synthetic polymeric flocculant used in the plant. The most influential factors were determined as flocculant concentration, first fast mixing speed and second gentle mixing speed. Subsequently, two response surface designs of experiments are constructed to investigate the optimal parameters of the factors. In the first design with three factors, optimal setting for the rapid mixing speed is identified at 250 RPM for 60 seconds and achieving values of 66.5% to 84.9% for suspended solids removal. After conducting the second response surface design, the final optimum dosage was determined at 0.9 mg/L flocculant concentration, second mixing phase program consisting of 155 RPM, 115 RPM, 75 RPM for a time duration of 15 minutes for the first two speeds in the program and 10 minutes from the last, followed by a 40 minute sedimentation period. The design successfully increased suspended solids removal to a range of 75.4% to 88.6%. Later on, four Polysaccharide based bio-flocculants are considered, Preliminary experiments results for SS removal showed high efficiency where a range of 84.8% to 89.5% was achieved. Utilizing the optimum dosage the %SS removal increased to a range of 92.60% to 97.76% and light transmission values ranging 73.46% to 87%, the results show great potential for these environmentally friendly flocculants to be implemented in the wastewater plant. Overall, manipulating the influential factors highlighted and implementing the optimal dosage identified in this research proved to produce satisfying results in terms of efficiency when tested for varying types of flocculants.
