abstract: The production and applications of engineered nanomaterials (ENM) has increased rapidly in the last decade, with release of ENM to the environment through the sewer system and municipal wastewater treatment plants (WWTPs) being of concern. Currently, the literature on ENM release from WWTPs and removal of ENM by WWTPs is insufficient and disorganized. There is little quantitative data on the removal of multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), or few-layer graphene (FLG), from wastewater onto biomass. The removal of pristine and oxidized MWCNTs (O-MWCNTs), graphene oxide (GO), few-layer graphene (FLG) and Tween™ 20-coated Ag ENM by the interaction with biomass were determined by programmable thermal analysis (PTA) and UV-Vis spectrophotometry. The removal of pristine and O-MWCNTs was 96% from the water phase via aggregation and 30-min settling in presence or absence of biomass with an initial MWCNT concentration of 25 mg/L. The removal of 25 mg/L GO was 65% with biomass concentration at or above 1,000 mg TSS/L. The removal of 1 mg/L FLG was 16% with 50 mg TSS/L. The removal of Tween™ 20 Ag ENM with concentration from 0.97 mg/L to 2.6 mg/L was from 11% to 92% with biomass concentration of 500 mg TSS/L to 3,000 mg TSS/L, respectively. A database of ENM removal by biomass was established by analyzing data from published papers, and non-linear solid-liquid distribution functions were built into the database. A conventional activated sludge (CAS) model was built based on a membrane bioreactor (MBR) model from a previous paper. An iterative numeric approach was adapted to the CAS model to calculate the result of non-linear adsorption of ENM by biomass in the CAS process. Kinetic studies of the CAS model showed the model performance changed mostly in the first 10 days after changing influent chemical oxygen demand (COD) concentration, and reached a steady state after 11 days. Over 60% of ENMs which have distribution coefficients in the database reached higher than 50% removal by the CAS model under general operational conditions. This result suggests that traditional WWTP which include the CAS process can remove many known types of ENMs in certain degree. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2015

Abstract This thesis aims to increase our knowledge about the characteristics of chemical pulp process and wastewaters and how problematic substances, e.g. wood extractives, could be removed effectively and selectively by coagulation–flocculation with either internal or external water treatment. Characterization was performed by investigating kraft pulp bleaching filtrates, as well as wastewater, before (influent) and after (effluent) the activated sludge treatment by means of a range of chemical analyses and by carrying out size fractionation studies. Cationic polyelectrolytes were used to purify oxygen stage bleaching filtrate, and charge analyses (zeta potential, charge quantity) were carried out in order to understand the coagulation phenomenon. In activated sludge treatment, the enhancement of particle removal, either by filtration or using a chemical in the primary clarifier, would lead to savings in aeration costs and result in a more stable process. Microfiltration already with a large pore size (8 µm) removed 30–50% of the wood extractives from the influent. Separate treatment stages for certain wastewater fractions, e.g. debarking plant effluent, would ensure cost-efficiency. After the activated sludge process, the wood extractives were present as particles (18%) and < 3 kDa fraction (82%). β-sitosterol occurred only in particles in the effluent. The release of harmful components into the environment could be decreased by microfiltration (e.g. 0.45 µm) of the final effluent or using a chemical in the secondary clarifier. Interestingly a huge increase in BOD was realized in the 3 kDa fraction of both influent and effluent, which indicated the presence of toxic substances in the larger fractions. After passing the effluent into the water system, there might be a similar jump in the BOD because the effluent is diluted many-fold. This would contribute to the formation of areas with an oxygen deficit. In the coagulation–flocculation studies, effective and selective removal of wood extractives (92%) from the oxygen stage filtrate was obtained with a cationic polyelectrolyte of medium molecular weight and medium charge density at 72 °C and pH 5–6. The multimodal zeta potential distribution gave more information than the average zeta potential. Aggregation of colloidal particles occurred when only one zeta potential was observed. The number of different zeta potentials diminished with decreasing pH and after exceeding a certain polyelectrolyte dosage level.

This master thesis gives an account for various aeration schemes that are utilized in conventional activated sludge treatment process in a wastewater treatment plant. By altering between different aeration schemes, the project aimed at reducing energy consumption along with maintaining the treatment performance at the plant. A series of experiments on the treatment performance over several different aeration schemes thus has been conducted on site at Solviken in Mora, Sweden. The project is basically a case study where no parameters were manually controlled except for the aeration schemes at the plant. Energy consumption reduction is logically relative to the ratio between aeration and non-aeration intervals. Several criteria were tested in regards to the treatment performance, including pH value, organic matters, phosphorus substances and microorganisms. The study has come up with a superior aeration scheme for the plant, as well as indicated processes that can be improved at the plant.