Karin Jönsson

Combined anaerobic–ozonation process for treatment of textile wastewater: Removal of acute toxicity and mutagenicity

A novel set up composed of an anaerobic biofilm reactor followed by ozonation was used for treatment of artificial and real textile effluents containing azo dyes. The biological treatment efficiently removed chemical oxygen demand and color. Ozonation further reduced the organic content of the effluents and was very important for the degradation of aromatic compounds, as shown by the reduction of UV absorbance. The acute toxicity toward Vibrio fischeri and the shrimp Artemia salina increased after the biological treatment. No toxicity was detected after ozonation with the exception of the synthetic effluent containing the highest concentration, 1 g/l, of the azo dye Remazol Red. Both untreated and biologically treated textile effluents were found to have mutagenic effects. The mutagenicity increased even further after 1 min of ozonation. No mutagenicity was however detected in the effluents subjected to longer exposure to ozone. The results of this study suggest that the use of ozonation as short post-treatment after a biological process can be beneficial for the degradation of recalcitrant compounds and the removal of toxicity of textile wastewater. However, monitoring of toxicity and especially mutagenicity is crucial and should always be used to assess the success of a treatment strategy.

Occurrence of nitrification inhibition in Swedish municipal wastewaters

The occurrence of substances inhibiting nitrification in Swedish municipal wastewaters was investigated using three methods: a screening method based on activated sludge and two pure culture methods based on Nitrosomonas and Nitrobacter. Influent samples from 109 wastewater treatment plants collected every day during one specific week were investigated. The three test methods were also compared. The results of the screening method showed that about 60% of the plants received wastewater containing inhibitory substances, although only 4% had considerable inhibition (>20%). With the two pure culture methods, inhibition was found at about 45% of the plants investigated, with considerable inhibition found at 13% and 20% of the plants with the Nitrosomonas and the Nitrobacter methods, respectively. The limit of detection was determined to be 5% inhibition for the screening method, 11% inhibition for the Nitrosomonas method and 13% inhibition for the Nitrobacter method. The pure culture methods found more samples strongly inhibitory or stimulating than the screening method. The highest correlation between the inhibition results from the three methods was found between the screening method and the Nitrosomonas method. It was also shown for sludge from several activated sludge treatment plants, that they were adapted to the toxic compounds present in the influent. At high inhibition this acclimatisation was less pronounced. No correlation was found for any of the methods between the inhibition and parameters such as the size of the plant, the geographic location, the content of ammonia, COD or conductivity in the influent, the presence of leachate or the percentage of industrial wastewater in the influent, or types of industries in the catchment area. However, the constantly highest inhibition was found at a plant with a large number of different industries connected. Any clear pattern for the variation of inhibition during the week was not found.

Anoxic biological phosphorus removal in a full-scale UCT process

Abstract Enhanced biological phosphorus removal is based on the selective enrichment of bacteria accumulating inorganic polyphosphate, obtained at a cyclic regime of alternating anaerobic and aerobic conditions. In the University of Cape Town (UCT) process for combined nitrogen and phosphorus removal, polyphosphate-accumulating bacteria will also be exposed to nitrate in the anoxic zone, i.e. an electron acceptor that may be utilized as well as the oxygen of the aerobic zone. During a 1-year study of the full-scale UCT process run at Oresundsverket, Helsingborg, special attempts were made to quantify the relative contribution of an anoxic phosphate uptake at full-scale conditions: the dominant chemical oxygen demand (COD) uptake in the anaerobic zone could be identified as poly-β-hydroxy-alkanoates (PHA). PHA accumulation was at its largest during a test period with acetate added as an extra carbon source. At least one-third of the COD consumed in the anoxic zone could be identified as PHA. The anoxic sludge contained increased amounts of polyphosphate and reduced amounts of free orthophosphate compared to the anaerobic zone, approaching the levels of aerobic sludge. The metal bound orthophosphate remained largely unaffected, at a level of 25–30% of the total phosphorus content. After correction for the sludge recycling of the system, the formation of inorganic polyphosphate in the anoxic zone itself was estimated to be 30% of the total. When the metabolic activity was tested under controlled conditions in batch, the anaerobic sludge of the plant showed a high denitrifying activity accompanied by a phosphorus uptake and a simultaneous consumption of intracellular PHA corresponding to 2 g-COD/g-N, i.e. half the theoretical value needed for denitrification when biomass growth is included. It is concluded that intracellular PHA played a major role as a carbon source for denitrification in this full-scale UCT process, with a corresponding phosphate uptake also in the anoxic zone. The biological nitrogen and phosphorus removal must, therefore, be regarded as interconnected.

Evaluating the Effect of Biofilm Thickness on Nitrification in Moving Bed Biofilm Reactors.

ABSTRACT This study evaluates the effect of biofilm thickness on the nitrifying activity in moving bed biofilm reactors (MBBRs) in a controlled environment. In-depth understanding of biofilm properties in MBBRs and their effect on the overall treatment efficiency is the key to optimizing process stability and efficiency. However, evaluating biofilm properties in continuously operated MBBRs can be extremely challenging. This study uses a carrier design which enables comparison of four different biofilm thicknesses, in otherwise equally operated lab-scale MBBRs. The results show that within the studied range (200–500 µm) and specific operation conditions, biofilm thickness alone had no significant effect on the overall ammonium removal. The nitrate production, however, decreased with a decreasing biofilm thickness, and the ratio between nitrite and ammonia-oxidizing activity decreased both with increasing load and decreasing oxygen concentration for all thicknesses. The suggestion that nitratation is disfavoured in thin biofilms is an interesting contribution to the current research being performed on nitrite-oxidizing bacteria inhibition for deammonification applications. By indicating that different groups of bacteria respond differently to biofilm thickness, this study accentuates the importance of further evaluation of these complex systems.

Utilising laboratory experiments as a first step to introduce primary sludge hydrolysis in full-scale

Laboratory experiments have been utilised as a tool to determine the possible yield of soluble COD and VFAs from settled influent and preprecipitated sludge at Klagshamn wastewater treatment plant and to determine the degradability of the organic matter. The release of ammonium and orthophosphate from the hydrolysed sludge has been estimated. It is possible to produce soluble organic matter of good quality from settled influent and preprecipitated sludge at Klagshamn WWTP. Denitrification rates of 3.1 mg NO3-N/(g VSS x h) were found for the hydrolysate in laboratory tests. Owing to the low phosphate concentrations in the hydrolysate from preprecipitated sludge, it shows a potential for postdenitrification despite stringent phosphorus outlet demands. Calculations based on data gained from the laboratory experiments show that about 50% of the external carbon source used today can be saved with minor changes in the plant operation except that the hydrolysis has to be established. Based on these findings, full-scale experiments with internal hydrolysis in the primary clarifiers were scheduled in one of the two lines at Klagshamn WWTP for the summer of 2007.

Carbon and phosphorus transformations in a full-scale enhanced biological phosphorus removal process

Carbon and phosphorus transformations in a full-scale enhanced biological phosphorus removal (EBPR) process was followed during 1 year. A correlation between the soluble phosphorus uptake in the process and the potential substrate for bio-P bacteria, measured as the volatile fatty acid (VFA) potential, in the influent wastewater was found. The results indicated that approximately 20 mg VFA-COD were required to remove 1 mg of soluble phosphorus. In the anaerobic stage of the process, poly-β-hydroxyalcanoic acids (PHA) were produced in an amount of 1.5 mg PHA-COD per mg of VFA-COD taken up by bio-P bacteria. Furthermore, a release of 0.31 mg of phosphate-P per mg of PHA-COD formed was observed in the anaerobic stage. Most of the released phosphate could be accounted for by a decrease in the polyphosphate content of the biomass in the anaerobic stage. Most of the results obtained were very well in agreement with the biochemical model for EBPR suggested by Smolders et al. (1994a).

Potential of combining mechanical and physicochemical municipal wastewater pre-treatment with direct membrane filtration

ABSTRACT At a full-scale wastewater treatment plant, raw municipal wastewater from the sand trap outlet was mechanically and physicochemically pre-treated before microfiltration (MF) in a large pilot-scale study. MF was performed using a low transmembrane pressure (0.03 bar) without backflushing for up to 159 h (∼6.6 d). Pre-filtration ensured stable MF operation compared with the direct application of raw wastewater on the membrane. The combination of physicochemical pre-treatment, such as coagulation, flocculation, and microsieving, with MF meets the European and Swedish discharge limits for small- and medium-sized wastewater treatment plants (WWTPs). The specific electricity footprint was 0.3–0.4 kWh·m−3, which is an improvement compared to the median footprint of 0.75 kWh·m−3 found in 105 traditional Swedish WWTPs with sizes of 1500–10,000 person equivalents. Furthermore, the biological treatment step can be omitted, and the risk of releasing greenhouse gases was eliminated. The investigated wastewater treatment process required less space than conventional wastewater treatment processes, and more carbon was made available for biogas production.

Identifying and fighting inhibition of nitrification at Öresundsverket

After extension of Oresundsverket in Helsingborg severe nitrification problems have occurred. Complete inhibition of nitrification has been recognized once and a general reduction of nitrification capacity has been found compared to design, to other Swedish treatment plants and to internationally accepted design criteria. A comprehensive examination of inhibition of nitrification has identified industrial sources as the dominating contributors. Some industries have been identified as important sources but fighting inhibition of nitrification requires more than tracking down a few dominating industries, since examination shows that discharges of inhibitory substances are widespread among the industries in the catchment area. Naturally, fighting inhibition of nitrification requires the elimination of contributions from industries with identified discharge. Furthermore information campaigns directed towards the industries in general are required and finally it is necessary to include requirements for inhibitory substances in the industrial discharge permits.

Determining short chain fatty acids in sewage sludge hydrolysate: a comparison of three analytical methods and investigation of sample storage effects.

In anaerobic digestion, the production of short-chain fatty acids (SCFAs) can be beneficial or harmful to the overall process, depending on the concentration of accumulated acids. Therefore, the accurate determination of the SCFA concentration in both fresh and stored sludge hydrolysates is important. To select a suitable method for monitoring SCFAs during the anaerobic digestion of sewage sludge, the accuracy of three available analytical methods, including 5 pH point acid titration (TITRA5), gas chromatography (GC), and spectrophotometry, were compared in the present study. The results revealed that TITRA5 and GC displayed better agreement in the achieved measurements and higher precision and accuracy than the spectrophotometric assay, as supported by the application of different statistical models. TITRA5 excelled in titrating unfiltered hydrolysate while simultaneously measuring the alkalinity, whereas the GC method provided detailed information on the contribution of different fatty acids to the total acidity. In contrast, the spectrophotometric assay suffered from many forms of interference, depending on the samples matrix. SCFA production followed the pattern of enzymatic reactions and fitted the Michaelis-Menten model. In addition to promoting TITRA5 as an accurate and robust analytical tool for routine SCFA analyses, this comparative study also demonstrated the possibility of storing hydrolysate samples at different temperatures and durations without altering the SCFA measurements.

Evaluation of direct membrane filtration and direct forward osmosis as concepts for compact and energy-positive municipal wastewater treatment

ABSTRACT Municipal wastewater treatment commonly involves mechanical, biological and chemical treatment steps to protect humans and the environment from adverse effects. Membrane technology has gained increasing attention as an alternative to conventional wastewater treatment due to increased urbanization. Among the available membrane technologies, microfiltration (MF) and forward osmosis (FO) have been selected for this study due to their specific characteristics, such as compactness and efficient removal of particles. In this study, two treatment concepts were evaluated with regard to their specific electricity, energy and area demands. Both concepts would fulfil the Swedish discharge demands for small- and medium-sized wastewater treatment plants at full scale: (1) direct MF and (2) direct FO with seawater as the draw solution. The framework of this study is based on a combination of data obtained from bench- and pilot-scale experiments applying direct MF and FO, respectively. Additionally, available complementary data from a Swedish full-scale wastewater treatment plant and the literature were used to evaluate the concepts in depth. The results of this study indicate that both concepts are net positive with respect to electricity and energy, as more biogas can be produced compared to that using conventional wastewater treatment. Furthermore, the specific area demand is significantly reduced. This study demonstrates that municipal wastewater could be treated in a more energy- and area-efficient manner with techniques that are already commercially available and with future membrane technology.