A study was conducted at a water treatment plant to optimize parallel rapid gravity biofilters for dissolved organic matter (DOM) removal. The biofilters treat urban and agriculturally impacted river water using a commercial non-adsorptive, expanded-clay filter medium. The study aimed to locate the optimal operating conditions via experimental manipulation of the biofilter empty bed contact time (EBCT) during full-scale operation at the plant. During a two-month experiment, contact times in four parallel biofilters were switched to and maintained at 15, 30, 50, and 80 min by manipulating the hydraulic loading on each filter. The removal efficiency of organic matter fractions increased with EBCT for dissolved organic carbon (DOC) and microbial humic-like (F290-420) and protein-like (F-280/340) fluorescent organic matter. Other DOM fractions were largely unaffected by biofiltration, or at slightly higher concentrations in the effluent. Protein-like fluorescence is associated with labile organic matter fractions, which are known to be removed poorly by drinking water treatment barriers apart from biological filters. The results suggest that long contact times (>30 min) have advantages for the operation of some biological filters, especially if placed ahead of barriers that are sensitive to biofouling, e.g., membranes.

Physical and chemical adsorption by aged biological active carbon (BAC) filters were observed for some organic matter fractions, and may represent important removal mechanisms during periods of low microbial activity.

Natural organic matter (NOM) in surface waters negatively impacts drinking water treatment and is a precursor of harmful disinfection by-products (DBPs). Granular activate carbon (GAC) filters are integral components of many drinking water treatment plants (WTPs) due to the ability to remove NOM and organic micro pollutants from raw waters. However, GAC filters lose adsorption capacity and convert to biologically activated carbon (BAC) filter relatively quickly. This paper reports on a full-scale BAC filter modification strategy to enhance short-term NOM removal. This is achieved by adding a small amount of fresh GAC to BAC filters which increases adsorption while maintaining biological degradation of organics by the microbes attached to the BAC. This strategy was implemented at two treatment plants in Sweden. Modified filters showed better removal of humic-like and protein-like NOM fractions than reference filters that did not receive fresh GAC, indicating improved functioning of both adsorption and biological treatment. The result shows that both biodegradation and adsorption mechanism improved within the filters.

There is a trend of increasing natural organic matter (NOM) in raw drinking waters of Nordic countries due to climate change. Seasonal deterioration in NOM quality imparts challenges for delivering a consistently high drinking water quality. In this study, a simple and cost effective operational strategy was investigated that improved short-term NOM removal in a full-scale treatment plant. Three granular activated carbon (GAC) media biofilters were modified by replacing a small fraction of saturated filter media with new media. Relative to replacing the entire biofilter media, this approach required lower capital cost and shorter downtime, and maintained conditions for biological filter functioning. NOM removal efficiencies were compared in modified versus unmodified (reference) filters using online UV absorbance, and offline fluorescence and dissolved organic carbon measurements. The modified biofilters showed improved organic matter removal lasting for at least four weeks. Partial replenishment of GAC in full-scale biofilters may be a useful and sustainable operational strategy for coping with temporarily high NOM loads in raw waters that might otherwise cause water quality problems.

Landfill leachates are repeatedly found contaminated with organic pollutants, such as alkylphenols (APs), phthalates and polycyclic aromatic hydrocarbons (PAHs) at levels exceeding water quality standards. It has been shown that these pollutants may be present in the colloidal and truly dissolved phase in contaminated water, making particle separation an inefficient removal method. The aim of this study was to investigate sorption and degradation of petroleum hydrocarbons (PHCs), selected APs, bisphenol A (BPA), phthalates and PAHs from landfill leachate using sand, granulated activated carbon (GAC) and peat moss filters. A pilot plant was installed at an inactive landfill with mixed industrial and household waste and samples were collected before and after each filter during two years.Leachate pre-treated in oil separator and sedimentation pond failed to meet water quality standards in most samples and little improvement was seen after the sand filter. These techniques are based on particle removal, whereas the analysed pollutants are found, to varying degrees, bound to colloids or dissolved. However, even highly hydrophobic compounds expected to be particle-bound, such as the PHCs and high-molecular weight PAHs, were poorly removed in the sand filter. The APs and BPA were completely removed by the GAC filter, while mass balance calculations indicate that 50-80% of the investigated phenols were removed in the peat filter. Results suggest possible AP degradation in peat filters. No evidence of phthalate degradation in the landfill, pond or the filters was found. The PHCs were completely removed in 50% and 35% of the measured occasions in the GAG and peat filters, respectively. The opposite trend was seen for removal of PAHs in GAG (50%) and peat (63%). Oxygenated PAHs with high toxicity were found in the leachates but not in the pond sediment. These compounds are likely formed in the pond water, which is alarming because sedimentation ponds are commonly used treatment techniques. The oxy-PAHs were effectively removed in the GAG, and especially the peat filter. It was hypothesized that dissolved compounds would adsorb equally well to the peat and GAC filters. This was not completely supported as the GAC filter was in general more efficient than peat. (C) 2014 Elsevier Ltd. All rights reserved.

In this thesis, a pilot plant to treat landfill leachate from contamination at Brudaremossen is designed, constructed and evaluated as preceding step before constructing a full scale plant on-site. Brudaremossen is a landfill site located near Lake Delsjon and leachates produced in this landfill are transferred to Goteborg’s wastewater treatment plant. Since leachate contains large quantities of harmful pollutants, it may affect the performance of the wastewater treatment process and quality of the sludge, and thus the leachates could preferable be treated locally. The organic pollutants of priority in the Brudaremossen landfill leachates are polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (oxy-PAHs), phthalates, alkylphenols (APs) and alkylphenolethoxylates (APEOs), and various petroleum hydrocarbon (PHC) fractions. The treatment technique chosen to study is sorption filtration, and the filter materials selected were activated carbon and Sphagnum peat moss. Two combinations of filter materials were examined: a column packed with granulated activated carbon (GAC) in series with another GAC column, and a column packed with peat moss followed by a column with GAC. Equal flow rates of the leachate were running through both combinations and the best alternative were identified based on the adsorbent performance. The plant was running for 120 days and influent and effluent concentrations to all the four filters were sampled weekly and selected samples analyzed for organic contaminants concentration. The result showed convincing performance in the adsorption of all the above mentioned organic pollutants. The GAC removed PHC fractions more efficiently (84-100%) than peat (31-52%), while peat was more efficiently adsorbing PAHs (14-61%). After two months of operation in-field, both of the filters indicate that PAHs, alkylphenols as well as phthalates were adsorbed effectively. Oxy-PAHs were removed efficiently by both filters. The GAC filter removed dissolved organic carbon (DOC) (85-100%) more effectively than the peat filter (2-28%), and total organic carbon (TOC) was removed well (5-100%) by both filter materials. The peat alternative overall reduced metals with better efficiency. The only complication during the operational period of the plant was the technical difficulties related to clogging of the filters due to too high concentration of iron and suspended particles. Therefore a sand filter was constructed before the filters, and influent and effluent samples from this filter were also analyzed for contaminants concentration. The need for a further pre-treatment is desirable because the sand filter was getting clogged too often and needed to be backwashed. Suggestions were made based on a laboratory test to aerate the leachates with the addition of CaCO3 as a suitable pre-treatment for the construction of the final treatment plant.