Long-term phosphorus and nitrogen removal processes and preferential flow paths in Northern constructed peatlands

Four treatment peatlands were studied in Northern Finland in order to determine peat P, Al and Fe concentration distributions and to find removal parameters for nutrient modelling. The sites had been under loading for 10–16 years. About 20 peat samples for analyses of oxalate-extractable and total P, Al and Fe were collected from the depth 0–10 cm in each peatland. The peat P concentration ranged from 0.097 mg g^?1 to 14 mg g^?1 being 1.7 mg g^?1on average. P accumulated in preferential flow path areas. Although P concentrations were locally high, DSSP (the index of potential soil P release from peat to water) was very low in all studied peatlands, indicating that peat was not saturated by phosphorus. The results indicate that Al-based precipitation chemicals increase substantially P retention capacity of peatland and maintain a stabile P reduction in spite of varying P loads. The results also show long-term phosphorus accumulation in peatlands polishing municipal wastewater from activated sludge treatment. The regression analyses showed that k-value for N removal depends on N loading and hydraulic loading. The first-order area model together with regression analysis of the rate constant result in a good agreement between observed and calculated nitrogen concentration. The NH₄-N loading to the peatland should be below 0.10 mg m² d^?1 in order to achieve a high reduction of 70%.     

Removal of Cu(II) ions by biosorption onto powdered waste sludge (PWS) prior to biological treatment in an activated sludge unit: A statistical design approach

Biological treatment of synthetic wastewater containing Cu(II) ions was realized in an activated sludge unit with pre-adsorption of Cu(II) onto powdered waste sludge (PWS). Box-Behnken experimental design method was used to investigate Cu(II), chemical oxygen demand (COD) and toxicity removal performance of the activated sludge unit under different operating conditions. The independent variables were the solids retention time (SRT, 5–30 d), hydraulic residence time (HRT, 5–25 h), feed Cu(II) concentration (0–50 mg L^?1) and PWS loading rate (0–4 g h^?1) while percent Cu(II), COD, toxicity (TOX) removals and the sludge volume index (SVI) were the objective functions. The data were correlated with a quadratic response function (R² = 0.99). Cu(II), COD and toxicity removals increased with increasing PWS loading rate and SRT while decreasing with the increasing feed Cu(II) concentration and HRT. Optimum conditions resulting in maximum Cu(II), COD, toxicity removals and SVI values were found to be SRT of 30 d, HRT 15 h, PWS loading rate 3 g h^?1 and feed Cu(II) concentration of less than 30 mg L^?1.     

Evaluation of phosphorus distribution and bioavailability in sediments of a subtropical wetland reserve in southeast China

The phosphorus (P) fractions and bioavailable P in the sediments from the Quanzhou Bay Estuarine Wetland Nature Reserve were investigated using chemical extraction methods for the first time to study the distribution and bioavailability of P in the reserve sediments. A hypothesis was presented suggesting that the bioavailable P in the sediments could be evaluated using the P fractions. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite phosphorus (NAIP), and apatite phosphorus (AP) contents in the sediments were in the ranges of 303.87–761.59 mg kg⁻¹, 201.22–577.66 mg kg⁻¹, 75.83–179.16 mg kg⁻¹, 28.86–277.90 mg kg⁻¹, and 127.36–289.94 mg kg⁻¹, respectively. The water soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algal available phosphorus (AAP), and NaHCO₃ extractable phosphorus (Olsen-P) contents in the sediments were in the ranges of 0.58–357.17 mg kg⁻¹, 80.77–586.75 mg kg⁻¹, 1.09–24.12 mg kg⁻¹, and 54.96–676.82 mg kg⁻¹, respectively. The correlation analysis results showed that the NAIP was the major component of the bioavailable P and that the impact of the AP on the bioavailable phosphorus may be minimal. Due to the low TP content in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve, the potential pollution risks of P in the sediments may not be very high. The results also show that the bioavailable P concentrations in the sediments of the Quanzhou Bay Estuarine Wetland Nature Reserve could not be evaluated by measuring the P fractions and that the hypothesis was untenable.     

Distribution of anammox bacteria in domestic WWTPs and their enrichments evaluated by real-time quantitative PCR

Enrichment of anaerobic ammonium oxidation (anammox) bacteria using five activated sludges in three domestic wastewater treatment plants (WWTPs) were processed in a short term of 70 days and evaluated by real-time quantitative PCR (RTQ-PCR). Before the enrichment, building phylogenetic trees of Planctomycetes phylum in four reactors of sequencing batch reactor (SBR), anoxic and oxic reactors of anaerobic–anoxic–oxic (A2O) process, and rotating biological contactor (RBC) revealed six groups of distantly relative genera of Planctomyces, Pirellula, Gemmata, Isophaera, Candidatus and putative anammox bacteria. All clones of Candidatus sp. were affiliated with anammox bacteria and the majority of anammox clones were related to Planctomycete KSU-1 (AB057453). The discovery of anammox bacteria in raw activated sludges provided a partial rationale for the utilization of activated sludge as a seeding source of the anammox process. To verify the activity of anammox bacteria in the activated sludges, enrichment cultivations were conducted using SBRs. The enrichment of anammox bacteria resulted in the significant anammox activity of three samples. Quantification of 16S rRNA gene of anammox bacteria using RTQ-PCR showed the highest concentration of anammox bacteria of 2.48 ± 0.22 × 10⁹ copies of 16S rRNA gene/mg-volatile suspended solids (VSS), which was the same order of magnitude as that of the referential granular anammox sludge, 6.23 ± 0.59 × 10⁹ copies of 16S rRNA gene/mg-VSS, taken from an anammox upflow anaerobic sludge blanket (UASB) reactor. The doubling time of anammox bacteria enriched in this study was 1.18 days. The growth yield of anammox bacteria enriched in this study was 4.75 ± 0.57 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen, which was similar to 4.50 ± 0.61 × 10⁶ copies of 16S rRNA gene/mg of ammonium- and nitrite-nitrogen for the referential anammox sludge. Substrate uptake rates of three successful enrichments at the end of the enrichment were comparable to those of granular and suspended anammox sludges. Rapid enrichment of anammox bacteria using activated sludge could offer an alternative method for obtaining a large volume of seeding anammox sludge.     

Dynamic simulation of a WWTP operated at low dissolved oxygen condition by integrating activated sludge model and a floc model

While an aeration tank in an activated sludge process is often operated with high dissolved oxygen (DO) concentration to ensure organic degradation and nitrification, it may be operated at low DO concentration to reduce energy consumption and achieve desired denitrification. The ASM1 (Activated Sludge Model No. 1) can be used to describe the activated sludge process if the nitrification and denitrification occur either during different phases or in different tanks, but it may encounter problems in simulating the denitrification phenomenon caused by low DO concentration in the aeration tank. In the present work, we developed a model integrating the ASM1 kinetics and a biofloc model to account for the actual anoxic and aerobic rates. Oxygen was assumed the only substrate of both bio-kinetically and flux limiting in the flocs and its dispersion coefficient was estimated as 1.2 × 10⁻⁴ m² day⁻¹ by using a set of measured effluent qualities of a full-scale wastewater treatment plant (WWTP) operating at low DO concentration (∼0.80 mg L⁻¹) for 60 days. Simulation studies predicted the optimal DO level of 0.36 mg L⁻¹ which would lead to minimum total nitrogen of 15.7 mg N L⁻¹ and also showed the insignificance of the addition of carbon source for nitrogen removal for the operation under study. The developed model may be helpful for process engineers to predict the plant behaviors under various configurations or operating strategies.     

Removal of triethylamine from synthetic wastewater by acclimated mixed bacteria cultures

This aim of this study was to remove triethylamine by a biological method, as well as to understand the ability of mixed bacteria cultures to treat a triethylamine compound from synthetic wastewater. The mixed bacteria cultures could not remove triethylamine, whether the activated sludge came from an acrylonitrile–butadiene–styrene resin manufactured wastewater treatment system or a waterborne polyurethane resin manufactured wastewater treatment system. When the mixed bacteria cultures were acclimated to triethylamine, they could utilize 650 mg l⁻¹ triethylamine for growth. When the initial triethylamine concentration was below 200 mg l⁻¹, the triethylamine removal efficiency could reach 100%. The triethylamine removal rate of the acclimated GMIX sludge was faster than the acclimated EMIX sludge.     

Management scenario evaluation for a large treatment wetland using a spatio-temporal phosphorus transport and cycling model

This paper describes the development of a two-dimensional, spatially distributed model to simulate coupled hydrologic and phosphorus (P) biogeochemical processes in a 147-ha cell of a 1544-ha stormwater treatment wetland designed to help protect the greater Everglades, FL, USA. The model was used to assess the effects of a suite of feasible management alternatives on the long-term ability of the wetland to sustain total P (TP) removal. The spatial and temporal dynamics of TP retention were simulated under historical (1995–2000) conditions, and under assumptions of removal of short-circuiting channels and ditches, changes in external hydraulic and TP loading, and long-term (>20 years) impacts on soil and water column TP dynamics under current and reduced load conditions. Internal hydrology and transport processes were calibrated against measured tracer concentrations, and subsequently validated against outflow discharge and spatial chloride concentration data. Cycling of P was simulated as first-order uptake and release, with different uptake coefficients for open water/sparse submerged aquatic vegetation (SAV) areas (0.2 day^?1) and dense SAV areas (0.4 day^?1), and a much lower, uniform release coefficient (1.97 × 10^?4 day^?1). The calibration and validation of the P model showed good agreement with field measurements of water column TP concentrations measured at the wetland outlet (calibration RMSE = 10.5 μg L^?1; validation RMSE = 15.6 μg L^?1). Under simulated conditions of preferential channels eliminated, average annual TP treatment effectiveness increased by 25%. When inflow TP loads were assumed to be eliminated after 6 years of loading, the release of accumulated soil P sustained predicted annual average outlet concentrations above 6.7 μg L^?1 for 18 years, decreasing at a rate of 0.16 μg L^?1 yr^?1. Sensitivity analyses indicate that the most critical model input factors include flow resistance parameters, initial soil TP content, and P cycling parameters compared to initial water level, initial TP concentration in water column, ET and transport parameters.     

A key cultivation technology for denitrifying granular sludge

Well-formed denitrifying granular sludge with a biomass concentration of 24.8 gVSS L^?1 and a specific nitrate removal rate of 0.19 gNO₃-N gVSS^?1 d^?1 was obtained in an upflow sludge blanket (USB) reactor by cultivating seeded aerobic flocculent sludge for 6–8 weeks. Regularity phenomena exist in the granulation including flotation of flocculent sludge, formation of fine granules, occurrence of channelling, and formation of mature granular sludge. The granulation is similar to crystal growth, that the non-denitrifying bacteria evolve into the carriers (fine granules), on the surface of which denitrifying bacteria proliferate and develop into mature granular sludge.There are several key parameters that must be considered when developing a good denitrifying granular sludge. First, the proper seed sludge must be chosen (VSS/SS at 0.65–0.75, SRT over 25 days) to accelerate the granulation process. Secondly, any floating sludge should be stirred, and the sludge loading rate should be within the range of 0.05–0.15 gNO₃-N gVSS^?1 d^?1 until fine granules emerge. Additionally, spontaneous gas agitation or interval air-blowing should be used to effectively eliminate channelling; Finally, the sludge loading rate should be less than 0.25 gNO₃-N gVSS^?1 d^?1 until dense, mature granular sludge appears. This study could support and promote the full-scale application of denitrifying granular sludge.     

Volatile fatty acids accumulation and rhamnolipid generation in situ from waste activated sludge fermentation stimulated by external rhamnolipid addition

The solubilization and acidification of waste activated sludge (WAS) were apparently enhanced by external rhamnolipid (RL) addition. The maximum solute carbohydrate concentrations increased linearly from 48 ± 5 mg COD L⁻¹ in the un-pretreated WAS (blank) to 566 ± 19 mg COD L⁻¹, and protein increased from 1050 ± 8 to 3493 ± 16 mg COD L⁻¹ at RL dosage of 0.10 g g⁻¹ TSS. The highest VFAs concentration peaked at 3840 mg COD L⁻¹ at RL dosage of 0.04 g g⁻¹ TSS, which was 4.24-fold higher than the blank test. RL was generated in situ during WAS fermentation when external RL was added. It was detected that RL concentration was increased from initial 880 ± 92 mg L⁻¹ to 1312 ± 7 mg L⁻¹ at the end of 96 h with RL dosage of 0.04 g g⁻¹ TSS, which was increased to 1.49-fold. Meanwhile, methane production was notably reduced to a quite low level of 2.0 mL CH₄ g⁻¹ VSS, showing effective inhibition of methanogens by RL (58.8 mL CH₄ g⁻¹ VSS in the blank). In addition, the activity of hydrolytic enzymes (protease and α-glucosidase) was enhanced accordingly. VFAs accumulation and RL generation in situ demonstrated that the additional RL substantially performed enhanced biological effects for waste activated sludge fermentation.     

Real-time control strategy for nitrogen removal via nitrite in a SHARON reactor using pH and ORP sensors

This paper presents a real-time control strategy for nitrogen removal via nitrite in a continuous flow SHARON reactor using on-line available and industrially feasible sensors (pH and ORP). The developed control strategy optimizes the length of aerobic and anoxic phases as well as the external carbon source addition. This strategy, implemented in a laboratory-scale SHARON reactor fed with synthetic wastewater and real dewatering sludge supernatant, was able to cope with step variations in influent flow rate and ammonium concentration. The main advantages of this control strategy over the traditional operation mode with fixed carbon source dosification and fixed length cycle operation were: better effluent quality (ammonia concentration decreased from 12 to 2 mg NH₄–N L^?1 and nitrogen removal efficiency raised from 95% to 98%) as result of the shorter cycle length: 2.9 h versus 4.0 h, and savings in external carbon addition: 1332 mg COD d^?1 versus 2100 mg COD d^?1.     

Bromophenol accumulation and sediment contamination by the marine annelids Notomastus lobatus and Thelepus crispus

The occurrence of bromophenols in Notomastus lobatus and Thelepus crispus and associated sediment and porewater was determined. 4-Bromophenol, 2,4-dibromophenol, and 2,4,6-tribromophenol were identified in N. lobatus with the highest concentrations occurring in the anterior and posterior abdomen and substantially less in the thorax (345, 209, and 6.6 μg/ml of worm, respectively). The concentration of dibromobenzyl alcohol was highest in the tail (last 15 setigers) of T. crispus (1.02 mg/ml of worm), but did not differ among body parts as the bromophenols did in N. lobatus. Concentrations in sediments were significantly reduced from those in the worms and decreased from the inner burrow lining out to 5 cm from N. lobatus burrows. Similarly for T. crispus, concentrations of dibromobenzyl alcohol in the surrounding sediments and porewater were low and increased with proximity to the burrow. For both species, concentrations in surface sediment (upper 1 cm) did not differ from those at 6 cm depth. Several lines of evidence indicate that these compounds are produced by the worms and hence their presence in sediments is derived from the worms. The contamination of sediment by these bromophenols has important implications for the structure and activities of benthic-associated communities.     

Modeling nutrients,oxygen and critical phosphorus loading in a shallow reservoir in China with a coupled water quality – Macrophytes model

Many macrophyte-dominated clear lakes switch to a phytoplankton-dominated turbid state when the lake becomes eutrophic. An existing Yuqiao Reservoir Water Quality Model (YRWQM) and the macrophyte submodel were coupled to simulate the effect of submerged macrophytes on nutrients and dissolve oxygen cycles in a shallow reservoir in China. The level of phosphorus loading in a transition from a clear to turbid state was addressed using the integrated model. The model runs from seedling establishment until dying out, from March 1 to July 18 in 2009. The simulations were performed for a contingent range of P loadings, starting from three different initial conditions. The results indicated that the integrated model improves accuracy of predictions compared to YRWQM. The concentrations of nutrients declined slightly during the macrophyte growth period in the reservoir and dissolved oxygen increased slightly. Although nutrient concentrations increased by submerged macrophyte release during the extinction period, the effect on the nutrients was less than that of transfer with nutrient-rich water. More released nutrients may enhance increases in substantial abundance. The critical phosphorus loading level during a switch from the clear to turbid state was estimated by these scenarios. The threshold for the switch is ∼6.1 mgP m⁻² d⁻¹ with an initial total phosphorus concentration of 160 μg l⁻¹. Moreover, the results demonstrated that the switch was also dependent on the initial total phosphorus concentration. These results suggest that the reservoir in a clear water state is at risk of a switch as nutrient levels are close to the critical levels.     

Bacterial decolorization and degradation of the reactive dye Reactive Red 180 by Citrobacter sp. CK3

A bacterial strain, CK3, with remarkable ability to decolorize the reactive textile dye Reactive Red 180, was isolated from the activated sludge collected from a textile mill. Phenotypic characterization and phylogenetic analysis of the 16S rDNA sequence indicated that the bacterial strain belonged to the genus Citrobacter. Bacterial isolate CK3 showed a strong ability to decolorize various reactive textile dyes, including both azo and anthraquinone dyes. Anaerobic conditions with 4 g l^?1 glucose, pH = 7.0 and 32 °C were considered to be the optimum decolorizing conditions. Citrobacter sp. CK3 grew well in a high concentration of dye (200 mg l^?1), resulting in approximately 95% decolorization extent in 36 h, and could tolerate up to 1000 mg l^?1 of dye. UV–vis analyses and colorless bacterial cells suggested that Citrobacter sp. CK3 exhibited decolorizing activity through biodegradation, rather than inactive surface adsorption. It is the first time that a bacterial strain of Citrobacter sp. has been reported with decolorizing ability against both azo and anthraquinone dyes. High decolorization extent and facile conditions show the potential for this bacterial strain to be used in the biological treatment of dyeing mill effluents.     

Estimation of the phosphorus requirement of weanling pigs fed supplemental phytase

Studies were conducted with crossbred weanling pigs to determine the level of phosphorus needed to be fed when a maize–soyabean meal–whey diet was supplemented with exogenous phytase (Natuphos™). In Trial 1, phytase was added at 1200 phytase units (PTU) kg⁻¹ as phosphorus decreased. The control diet in Phase I (0–14 days) contained 7.3 g kg⁻¹ phosphorus and in Phase II (14–28 days) contained 6.5 g kg⁻¹ phosphorus. Dietary phosphorus was calculated to decrease by 0.8, 1.6 or 2.4 g kg⁻¹ when phytase was supplemented. Chromic oxide was added for estimation of apparent absorption of phosphorus. Performance was optimum when 5.7 and 4.8 g kg⁻¹ phosphorus (analysed levels) were fed with 1200 PTU kg⁻¹ phytase in Phases I and II, respectively. The lowest dietary phosphorus levels did not reduce performance for the overall 28-day period. Apparent phosphorus digestibility was increased by phytase in Phase I when 5.7 g kg⁻¹ phosphorus was fed compared to the control diet and in Phase II when 6.0 g kg⁻¹ phosphorus was fed with phytase. Faecal phosphorus excretion decreased in both phases as dietary phosphorus decreased. Faecal phosphorus excretion was minimized at the lowest phosphorus level with no decrease in performance. The estimated requirement for dietary phosphorus, as determined by the NLIN procedure, is 5.0 g kg⁻¹ in Phase I and 4.3 g kg⁻¹ in Phase II when 1200 PTU kg⁻¹ is used. In Trial 2, phytase was supplemented at 500 PTU kg⁻¹ when phosphorus was decreased in the diet. The control diet contained 6.6 and 6.0 g kg⁻¹ phosphorus in Phases I and II, respectively, and phosphorus was calculated to decrease by 0.5, 1.0, 1.5, or 2.0 g kg⁻¹ when phytase was added. Daily gain decreased when 5.0 g kg⁻¹ phosphorus was fed in Phase I and when 4.6 or 4.2 g kg⁻¹ (analysed levels) phosphorus was fed in Phase II with 500 PTU kg⁻¹. Faecal phosphorus excretion decreased as dietary phosphorus decreased, but there were no treatment effects on apparent phosphorus digestibility. The dietary phosphorus requirement was estimated to be 5.7 and 5.0 g kg⁻¹ in Phases I and II, respectively, when phytase is fed at 500 PTU kg⁻¹. At the present recommendation of 500 PTU kg⁻¹ in starter feed, phosphorus can be decreased by 0.10 g kg⁻¹. However, higher levels of phytase are needed to actually increase apparent phosphorus digestibility.     

Dominance of yeast in activated sludge under acidic pH and high organic loading

Flow cytometry-fluorescent in situ hybridization (FC-FISH) was used to investigate the effect of controlled pH and/or varied organic loading on the content of yeast and bacterial cells in an activated sludge system (AS) individually operating in continuous and batch mode for treatment of high-strength industrial wastewater. Specifically, we attempted to develop a yeast-predominant activated sludge system (Y-AS). For the batch-mode AS, bacteria-dominated AS (B-AS) obtained at pH 6.5–7.5 induced higher chemical oxygen demand (COD) removal than Y-AS obtained at acidic pH (5.0–6.0 and 4.0–5.0). For the continuous-mode AS operating at COD loadings of 2.5–2.8 kg COD m⁻³ d⁻¹, it was difficult to achieve a Y-AS solely by controlling the pH level at 7.0 to 5.1 then to 4.1 because bacteria stably accounted for greater than 98% of the total cells, regardless of the pH levels. Therefore, the effects of varied COD loadings (2.1, 8.7 and 21.0 kg COD m⁻³ d⁻¹) on continuous-mode AS operation at acidic pH (4.5) was investigated. Both acidic pH and high COD loading levels were found to be prerequisites for yeast to dominate the sludge microbial community in the continuous-mode AS.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Effects of experimental warming and nitrogen enrichment on leaf and litter chemistry of a wetland grass,Phragmites australis

As global climate is warming and the nitrogen cycle accelerates, plants are likely to respond not only by shifting community composition, but also by adjusting traits such as tissue chemistry. We subjected a widespread wetland plant, Phragmites australis, to increased nitrate supply and elevated temperature in enclosures that were established in a littoral permanently submerged freshwater marsh. The nitrogen (N) and phosphorus (P) concentrations in green leaves ranged from 11.4 to 13.8 mg N and from 1.5 to 2.0 mg P g⁻¹ dry mass. While the N concentration changed little in brown litter, the P concentration decreased to 0.53–0.65 mg P g⁻¹ litter dry mass. Neither experimental warming of the water and sediment surface, nor nitrate enrichment during the growing season affected nitrogen or phosphorus concentrations in green leaves. Concentrations of the two major structural carbon compounds in plant litter, cellulose and lignin, were also unaffected, ranging from 32.1 to 34.2% of dry mass for cellulose and from 16.3 to 17.7% of dry mass for lignin. Warming, however, significantly increased the nitrogen concentration of fully brown leaf litter. Thus, temperature appears to be more important than the supply of dissolved N in the water, especially in affecting leaf litter N concentrations in P. australis, even when only water but not air temperature is increased. This result may have implications for decomposition processes and decomposer food webs, which both depend on the quality of plant litter.     

Investigation on the formation and kinetics of glucose-fed aerobic granular sludge

Aerobic granular sludge was cultivated in a glass sequencing batch reactor (SBR) with glucose synthetic wastewater. The spherical shaped granules were observed on 4th day with the mean diameter of 0.1 mm. With the increase of chemical oxygen demand (COD) concentration of the influent, aerobic granules grew matured, the size of which ranged from 1.2 to 1.9 mm. The aerobic granular sludge could sustain high organic loading rate (about 4.0 g COD L⁻¹ d⁻¹), with good settling ability (settling velocity 36 m/h) and high biomass concentration (MLSS 6.7 ±0.2 g/L). Experimental data indicated that the substrate utilization and biomass growth kinetics followed Monod's kinetics model approximately. The corresponding kinetic coefficients of maximum specific substrate utilization rate (k), half velocity coefficient (K_s), growth yield coefficient (Y) and decay coefficient (K_d) were 13.2 d⁻¹, 275.8 mg/L, 0.183–0.250 mg MLSS/mg COD and 0.023–0.075 d⁻¹, respectively, which made aerobic granules have short setup period, high rate of substrate utilization and little surplus sludge.     

Characterization of aerobic granular sludge at various organic loading rates

Aerobic granular sludge was cultivated from activated sludge with two types of supports, namely bivalve shell carrier (BSC) and anaerobic granules (ANG). Granules were characterized at different organic loading rates (OLRs) ranging from 2.5 to 15 kg COD/m³ d and these granules were observed to withstand high OLRs. The physico-chemical characteristics of the aerobic granules were better than those of seed sludge. The granule formation with ANG support was found to be similar to that of non-support cultivation, i.e. formation from activated sludge only. By contrast, BSC support showed better performance in terms of faster settleability, compactness and especially resistance against organic shock loading. It also enabled self-cleaning effect by removing biofilm attached on the reactor wall during the start-up phase resulting rapid granulation process.     

The performance of peat-filled subsurface flow filters treating landfill leachate and municipal wastewater

The main objective of this study was to determine the treatment capacity of well-mineralized peat in vertical and horizontal flow filters designed to reduce phosphorus, nitrogen and organic matter in municipal wastewater from the town of Tapa and landfill leachate in Väätsa, Estonia. Two identically designed onsite experiments were conducted using the following filter systems: (a) a vertical flow (VF) peat filter, (b) a vertical flow peat/ash sediment filter (both materials in equal volumes) followed by a horizontal flow (HF) peat filter. Sphagnum peat and hydrated oil-shale ash (ash sediment) was used. In our experiments, one treated municipal wastewater over 6 months and another treated landfill leachate over 12 months. In both cases, effluent from a conventional treatment (aerated activated sludge treatment) plant was used. The median value of total phosphorus (TP) concentration in Väätsa landfill leachate was 3.4 mg P L^?1 and in municipal wastewater from Tapa 4.9 mg P L^?1. The reduction of TP in VF peat filters during the first 6 months was 58% and 63%, and in peat/ash sediment filters 94% and 67% for the Tapa experiment and the Väätsa experiment, respectively. Both experiments demonstrated that the P-removal efficiency in VF peat filters begins to decrease after 6 months of operation. The purification efficiency in HF filters fluctuated, and no significant removal of TP was found. In the removal of organic matter (BOD, COD values) and nitrogen, the best results were obtained in VF peat filters.