Effect of wastewater step-feeding on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands

The performance of a pilot-scale horizontal subsurface flow (HSF) constructed wetland is investigated with emphasis on the effects of wastewater step-feeding. One pilot-scale unit, of dimensions 3 m in length and 0.75 m in width, operated continuously from January 2004 until February 2007. The unit contained cobbles obtained from a river bed and was planted with common reed (Phragmites australis). Synthetic wastewater was introduced to the unit. During the first two years of operation (period A) one inflow point was used at the upstream end of the unit. During the third year of operation (period B), wastewater step-feeding was adopted. Wastewater was introduced to the unit through three inlet points: one at the upstream end of the unit length and the other two at 1/3 and 2/3 of the unit length. Two wastewater step-feeding schemes were examined during the second working period: 33:33:33 and 60:25:15. Three HRTs (6, 8 and 14 days) were applied; wastewater temperatures varied from 6.0 to 25.0 °C. On the whole, the adoption of step-feeding in a HSF CW may be positive if an appropriate scheme is selected. Indeed, the removal of organic matter (BOD₅ and COD), nitrogen (TKN and ammonia) and phosphorus (Total Phosphorus and ortho-phosphate) was improved under the step-feeding Scheme 60:25:15, while the other scheme (33:33:33) affected negatively the wetland performance.     

Treatment of olive mill wastewater in pilot-scale vertical flow constructed wetlands

Pilot-scale constructed wetlands (CW) were constructed and operated to treat pre-treated olive mill wastewater. Pilot-scale units comprising three identical series with four pilot-scale vertical flow CWs were operated for one harvest season in a Greek olive mill plant. The pilot-scale CWs were filled with various porous media (i.e., cobble, gravel, and sand) of different gradations. Two series of pilot-scale units were planted with common reeds and the third (control) was unplanted. Mean influent concentrations were 14,120 mg/L, 2841 mg/L, 95 mg/L, 123 mg/L and 506 mg/L for COD, phenols, ortho-phosphate, ammonia and TKN, respectively. Despite the rather high influent concentrations, the performance of the CW units was very effective since it achieved removals of about 70%, 70%, 75% and 87% for COD, phenols, TKN and ortho-phosphate, respectively. COD, phenol and TKN removal seems to be significantly higher in the planted series, while ortho-phosphate removal shows no significant differences among the three series. Temperature and pollutant surface load seem to affect the removal efficiency of all pollutants. Compared to previous studies, pollutant surface loads applied here were higher (by one or two orders of magnitude). Even though high removal efficiencies were achieved, effluent pollutant concentrations remained high, thus preventing their use for irrigation or immediate disposal into the environment.     

Enhanced denitrification and organics removal in hybrid wetland columns: comparative experiments

This study investigated three lab-scale hybrid wetland systems with traditional (gravel) and alternative substrates (wood mulch and zeolite) for removing organic, inorganic pollutants and coliforms from a synthetic wastewater, in order to investigate the efficiency of alternative substrates, and monitor the stability of system performance. The hybrid systems were operated under controlled variations of hydraulic load (q, 0.3-0.9 m³/m² d), influent ammoniacal nitrogen (NH₄-N, 22.0-80.0 mg/L), total nitrogen (TN, 24.0-84.0 mg/L) and biodegradable organics concentration (BOD₅, 14.5-102.0 mg/L). Overall, mulch and zeolite showed promising prospect as wetland substrates, as both media enhanced the removal of nitrogen and organics. Average NH₄-N, TN and BOD₅ removal percentages were over 99%, 72% and 97%, respectively, across all three systems, indicating stable removal performances regardless of variable operating conditions. Higher Escherichia coli removal efficiencies (99.9%) were observed across the three systems, probably due to dominancy of aerobic conditions in vertical wetland columns of the hybrid systems.     

Treatment of domestic and agricultural wastewater by reed bed systems

The purification capacity and seasonal variability of two newly created reed bed systems was monitored over 1 year. In one of the systems treating domestic wastewater, the reduction in the concentrations of chemical oxygen demand (COD), total N, total P and fecal coliform bacteria (FC) ranged from 80 to 99%. In the second system, treating a mixture of domestic and agricultural wastewater produced by a cheese dairy, treatment efficiency ranged between 13 and 99%. The removal rates did not show any seasonal pattern for domestic wastewater, in contrast to the mixture of domestic and agricultural wastewater with increased removal rates in the summer. Bacteria which are involved in N metabolism was estimated by the most probable number-test (MPN). In both reed bed systems the MPN of proteolytic bacteria, ammonifiers, nitrifiers and denitrifiers/g DW of gravel substrate were of the orders of magnitude of 10⁴–10⁶, 10⁵–10⁷, 10¹–10⁵ and 0–10³, respectively. On the basis of the microbial assemblage there is a need to improve the conditions for both nitrification and denitrification to enhance the efficiency of N removal.     

Chlorobenzene removal efficiencies and removal processes in a pilot-scale constructed wetland treating contaminated groundwater

Low-chlorinated benzenes (CBs) are widespread groundwater contaminants and often threaten to contaminate surface waters. Constructed wetlands (CWs) in river floodplains are a promising technology for protecting sensitive surface water bodies from the impact of CBs. The efficiency and seasonal variability of monochlorobenzene (MCB), 1,4-dichlorobenzene (1,4-DCB) and 1,2-dichlorobenzene (1,2-DCB) removal, the impact of planting, and gaseous MCB emissions from the filter surface were investigated over the course of 1 year in both a vegetated pilot-scale CW and an unplanted reference plot (UR). Annual mean concentration decreases of MCB and 1,4-DCB were observed; however, annual mean 1,2-DCB removal was seen only in the upper filter layer. Planting (Phragmites australis) had a statistically significant beneficial effect on removal. The CB removal efficiency in the CW generally decreased with depth, and seasonal variations of removal were evident, with less concentration decrease during summer. Load removal efficiencies of 59-65% (262-358 mg m⁻² d⁻¹) for MCB, 59-69% (4.0-5.1 mg m⁻² d⁻¹) for 1,4-DCB and 29-42% (0.6-2.1 mg m⁻² d⁻¹) for 1,2-DCB were observed in June and July. Volatilization of MCB from the filter surface accounted for 2-4% of the total amount removed. Simple cover layers of organic materials on the filter surface were suitable for MCB emission reduction. Model calculations were carried out to estimate the MCB removal potential attributable to microbial degradation, volatilisation, and plant uptake in the CW and UR. Microbial degradation was the dominating process. The observed positive impact of plants on MCB removal was caused by improved oxygen supply (due to root oxygen release into the rhizosphere and enhanced water table fluctuations), and direct plant uptake.     

Estrogen removal from treated municipal effluent in small-scale constructed wetland with different depth

The presence of estrone (E1), 17 beta-estradiol (E2) and 17 alpha-ethynylestradiol (EE2) in sewage treatment work (STW) effluent pose a potential risk to aquatic ecosystem. The objectives of this study were to evaluate the effectiveness of vertical-flow wetland as polishing step of conventional wastewater treatment in the removal of estrogens and to examine the effect of sand depth. The highest removal efficiency of 67.8 ± 28.0%, 84.0 ± 15.4% and 75.3 ± 17.6% for E1, E2 and EE2, respectively, was achieved by the shallowest wetland among three constructed wetlands with different filter layer depth (i.e. 7.5, 30 and 60 cm). Together with the result that the performance of wetlands when operating in unsaturated condition was superior to that when operating in water-saturated condition, it is suggested that maintaining sufficient aerobic circumstance in constructed wetlands was important for estrogens removal. Core sampling indicated that the highest efficiency achieved in extremely shallow wetland might be due partly to the highest root density, besides the superior condition for penetration of oxygen. The adsorbed estrogens in sand accounted for less than 12% of the removed estrogens irrespective of the depth, indicating biotic processes play a major role in the estrogens removal.     

Nitrogen and potassium variation on contaminant removal for a vertical subsurface flow lab scale constructed wetland

Lab scale constructed wetlands were used to evaluate organic load removal efficiency. Bioreactors were fed with synthetic wastewater (SW) with varying concentrations of nitrogen and potassium. Reactors were planted with species Phragmites australis. Fed theoretic COD was adjusted to 240.0 mg-O₂ L⁻¹, nitrogen levels were 10 and 40 mg-N L⁻¹ (ammonium sulfate), potassium levels were 5 and 31 mg-K L⁻¹ (potassium monobasic phosphate). The higher biomass yield, for 0.5 and 0.775 N:K ratios, was related with higher organic load removal. The ratio N:K showed significant differences for organic load abatement, when 1:0.5 and 1:0.775 N:K ratios were applied, 96.8% efficiency was obtained, whereas N:K ratio of 1:0.125 had efficiency of 92.1% and N:K ratio of 1:3.1 showed an efficiency of 90.5%. For planted bioreactor E_H decreased in 162.7 mV from sample port to 5 cm down to 35 cm depth, while for the bioreactor without plant showed an E_H decrement of only 17.7 mV.     

Schoolhouse wastewater purification in a LWA-filled hybrid constructed wetland in Estonia

This paper analyses the purification efficiency and mass removal of organic material, suspended solids, nitrogen and phosphorus in a hybrid constructed wetland (CW) system treating wastewater from a basic school in Paistu, Estonia. The CW consists of two subsurface flow filter beds using lightweight aggregates (LWA): a two-chamber vertical subsurface flow (VSSF) filter bed followed by a horizontal subsurface flow (HSSF) filter bed, with a total area of 432 m². This CW was constructed in summer 2002 by the Centre for Ecological Engineering in Tartu (CEET). Eighteen series of water samples (from 30.10.2003 to 15.10.2005) were undertaken. The analyses show the outstanding purification effect of the system: for BOD₇ the average purification efficiency is 91%; for total suspended solids (TSS)—78%, for total P—89%, for total N—63%, and for NH₄N—77%. The average outlet values for the above-listed parameters were 5.5, 7.0, 0.4, 19.2 and 9.1 mg L⁻¹, respectively. According to our results, the purification parameters meet the standards set by the Water Act of Estonia for wastewater treatment plants of 2000–9999 PE: 15, 25, and 1.5 mg L⁻¹ for BOD₇, TSS and total P, respectively. The results show that hybrid CW systems consisting of subsurface flow filter beds can work efficiently in conditions of changing hydraulic loading and relatively cold climate. We did not find significant differences between the removal efficiency, mass removal, and values of the first-order rate-constant k for most water quality indicators during the warm (May–October) and cold (November–April) periods. Locally produced LWA as a filter material in CWs has shown good hydraulic conductivity and phosphorus sorption capacity (k = 17.1 ± 12.4 m yr⁻¹). The Paistu CW, with its proper design and outstanding purification results, can be considered one of the best systems in Estonia.     

A three-stage experimental constructed wetland for treatment of domestic sewage: First 2 years of operation

Hybrid constructed wetland systems have recently been used to treat wastewaters where high demand for removal of ammonia is required. However, these systems have not been used too often for small on-site treatment systems. This is because in many countries ammonia is not limited in the discharge from small systems. Hybrid systems have a great potential to reduce both ammonia and nitrate concentrations at the same time. In our study we employed a three-stage constructed wetland system consisting of saturated vertical-flow (VF) bed (2.5 m², planted with Phragmites australis), free-drained VF bed (1.5 m², planted with P. australis) and horizontal-flow (HF) bed (6 m², planted with Phalaris arundinacea) in series. All wetlands were originally filled with crushed rock (4-8 mm). However, nitrification was achieved only after the crushed rock was replaced with sand (0-4 mm) in the free-drain wetland. Also, original size of crushed rock proved to be too vulnerable to clogging and therefore, in the first wetlands the upper 40 cm was replaced by coarser fraction of crushed rock (16-32 mm) before the second year of operation started. The system was fed with mechanically pretreated municipal wastewater and the total daily flow was divided into two batches 12 h apart. The evaluation of the results from the period 2007 to 2008 indicated that such a system has a great potential for oxidation of ammonia and reduction of nitrate. The ammonia was substantially reduced in the free-drained VF bed and nitrate was effectively reduced in the final HF bed. The inflow mean NH₄-N concentration of 29.9 mg/l was reduced to 6.5 mg/l with the average removal efficiency of 78.3%. At the same time the average nitrate-N concentration rose from 0.5 to only 2.7 mg/l at the outflow. Removal of BOD₅ and COD amounted to 94.5% and 84.4%, respectively, with respective average outflow concentrations of 10 and 50 mg/l. Phosphorus was removed efficiently despite the fact that the system was not aimed at P removal and therefore no special media were used. Phosphorus removal amounted in 2008 to 65.4%, but the average outflow concentration of 1.8 mg/l is still high. The results of the present study indicate very efficient performance of the hybrid constructed wetlands, but optimal loading parameters still need to be adjusted. The capital cost of the experimental system is comparable to the conventional on-site treatment plant but the operations and maintenance costs are about one third of the conventional plant.     

Nitrogen transformation in two subsurface infiltration systems at pilot scale

Nitrogen removal and transformations were studied in two pilot-scale combinations of a special configuration of a subsurface wastewater infiltration system with vertical flow named symbiotic treatment^®. Both pilot-scale combinations operated in parallel and each one consists of four stages in series, one of them with a vertical distribution of stages and the other one with a horizontal distribution. The main differences between them were the separation between stages (presence (the horizontal distribution)/absence (the vertical distribution) of filtration between steps), the hydraulic load (0.113 m³/m² h and 0.082 m³/m² h for the horizontal and the vertical distribution, respectively) and the depth of the soil filters (1 m each stage in the horizontal distribution whereas the depths in the vertical distribution ranges from 20 cm to 40 cm). Results of both configurations showed elevated dissolved oxygen concentration, and high removal of organic matter and total suspended solids (with mean removal values of 96% for COD for both plants and 90% and 98% for TSS for the vertical and the horizontal distribution, respectively). High total Kjeldahl nitrogen removals were obtained in both configurations (mean removals of 70% and 90% for the vertical and the horizontal distribution, respectively). Whereas the nitrification potential was higher in the configuration with horizontal distribution which includes pumping and filtering between stages and higher depth of the soil filters, both tested configurations showed promise for nitrification of wastewater, ammonia nitrogen was efficiently transformed to nitrate.     

Influence of vegetation and substrate on the removal and transformation of dissolved organic matter in horizontal subsurface-flow constructed wetlands

The fate of dissolved organic matter (DOM) during horizontal subsurface-flow constructed wetlands (HSSF CWs) was examined. In several studies it had been demonstrated that factors such as vegetation and substrates type affected the treatment efficiency of DOM, while very few studies discerned their influence on the transformations of DOM. Thus three pilot-scale HSSF CWs, i.e. reed (Phragmites australis)/gravel bed (W1), hybrid vegetation{cattail (Typha latifolia), bulrush (Scirpus validus), reed}/gravel bed (W2) and reed/hybrid substrates bed (gravel, zeolite, slag) (W3), were designed, and were operated continuously to investigate soluble COD (SCOD) removal and DOM transformations affected by vegetation and substrate type, and to explore the correlation between SCOD and biodiversity. The results showed that cattail and bulrush contributed to higher SCOD removal than common reed, and that gravel, zeolite and slag did not show significant influence on SCOD removal. The composition of the dissolved organic carbon (DOC) could undergo a considerable shift in composition due to metabolism and senescence from plant and microorganism. Nonlabile aromatic hydrocarbons and alkyl hydrocarbons in the effluent were a significant portion compared with labile alcoholic and alkene in the influent. It was also observed that the type of vegetation and substrate had great influence on the structure of bacteria, and the Shannon-Wiener Index increased linearly with the decrease of SCOD concentration along water flow in W2 and W3 (R2=0.96).     

Enhanced denitrification in a bioaugmented horizontal subsurface flow filter

The effect of adding low concentrations of a sediment/microbial community suspension to speed up the development of the denitrification capacity in the restored HSSF of a hybrid CW was studied during a one-year period after the filling of the horizontal filter with new light weight aggregates (LWA). Two HSSF filters with the same LWA substrate but different wastewater flow regimes were used as donor systems for the bioaugmentation. NO₃-N concentrations in the outflows of all variants of studied MCs were significantly influenced by the time factor (p < 0.001, repeated measures ANOVA). Post hoc comparison indicated that MCs bioaugmented with the sediment suspension from a similar HSSF had significantly lower NO₃-N concentrations than the control MCs (p < 0.05, Fisher LSD test), whereas MCs bioaugmented with the sediment suspension from a less similar HSSF did not show significant differences compared to the control MCs. This finding emphasizes the importance of the similarity of flow regime and water parameters in choosing a donor system for bioaugmentation. High variability of the effect of bioaugmentation shows that its importance for full scale operation may be overshadowed by the effect of other factors determining denitrification intensity.     

Removal of pharmaceutical compounds in tropical constructed wetlands

The ability of tropical horizontal subsurface constructed wetlands (HSSF CWs) planted with Typha angustifolia to remove four widely used pharmaceutical compounds (carbamazepine, declofenac, ibuprofen and naproxen) at the relatively short hydraulic residence time of 2-4 days was documented. For both ibuprofen and naproxen, pharmaceutical compounds with low D_ow values, the planted beds showed significant (p < 0.05) enhancement of removal efficiencies (80% and 91%, respectively, at the 4 day HRT), compared to unplanted beds (60% and 52%, respectively). The presence of plants resulted in the removal of these pharmaceutical compounds from artificial wastewater. The more oxidizing environment in the rhizosphere might have played an important role, but other rhizosphere effects, beside rhizosphere aeration, appeared to be important also. Carbamazepine, considered one of the most recalcitrant pharmaceuticals, and declofenac showed low removal efficiencies in our CW, and this is attributable to their higher hydrophobicity. The fact that the removal of these compounds could be explained by the sorption onto the available organic surfaces, explains why there was no significant difference (p > 0.05) in their removal efficiencies between planted as compared to unplanted beds. No statistical significant differences (p > 0.05) were observed for the removal efficiencies of any of the pharmaceuticals tested for the 2-day HRT as compared to that corresponding to 4-day HRT. The rather efficient removal shown by the wetlands in this study (with HRTs of 2-4 days), indicates that such a CW system may be more practically used (with less land requirements) in tropical regions for removing conventional pollutants and certain pharmaceutical compounds from wastewater effluents.     

Culture of Scenedesmus sp. LX1 in the modified effluent of a wastewater treatment plant of an electric factory by photo-membrane bioreactor

To investigate the coupled technology for advanced wastewater treatment and microalgal biomass production, a photo-membrane bioreactor was constructed. The microalga Scenedesmus sp. LX1 was cultured in the bioreactor using liquor prepared from the effluent of an electronic device factory. The algal cell growth, nitrate nitrogen removal, orthophosphate phosphorus removal were investigated. When cultured with batch operation, the average specific growth rate was about 0.09 d⁻¹, and low nitrogen (N), phosphorus (P) concentrations in the liquor were achieved. However, under continuous operation with an inflow of 60 L h⁻¹, the average specific growth rate was only 0.02 d⁻¹, and removal rates of 100% for orthophosphate P and 46% for nitrate N were achieved. With the inflow of 120 L h⁻¹, the accumulated metal ions in the bioreactor adversely affected the algal cells. The algal cells were much easier to settle, and the removal efficiency for N and P decreased.     

Enhancement of nitrogen removal in towery hybrid constructed wetland to treat domestic wastewater for small rural communities

Efforts to protect watercourses, especially sources of drinking water, particularly in rural areas, are now underway in China. Nitrogen present in wastewater, due to its role in eutrophication and potential toxicity to aquatic species, is a focus of primary concern. Constructed wetlands (CWs), a simpler, less costly treatment alternative, have been used to treat domestic wastewater for small communities. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been successful in removing nitrogen mainly due to lack of dissolved oxygen (DO). To enhance nitrogen removal, a novel CW configuration with three stages, towery hybrid constructed wetland (THCW), was designed. The first and third stages were rectangle subsurface horizontal flow CWs, and the second stage was a circular three-layer free-water flow CW. Increased DO by passive aeration of a tower type cascade overflow from the upper layer into the lower layer in the second stage of the wetland enhanced nitrification rates. Denitrification rates were also improved by additional organic matter supplied as a result of bypass influent directly into the second stage. Evergreen tree Pond Cypress (Taxodium ascendens), industrial plants Mat Rush (Schoenoplectus trigueter) and Wild Rice shoots (Zizania aquatica), ornamental floriferous plants Pygmy Waterlily (Nymphaea tetragona) and Narrow-leaved Cattail (Typha angustifolia) were planted in the wetland. The average percentage of removal was 89%, 85%, 83%, 83% and 64% for total suspended solid, chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus, respectively. There was no significant difference (p < 0.05) at low and high hydraulic loads (16 cm/d and 32 cm/d) for performance of THCW. Nitrifying and denitrifying bacteria as well as potential nitrification activity and potential denitrification rates measured have shown that nitrification–denitrification is the main mechanism for nitrogen removal in the wetland. THCW also provided additional aesthetic benefits.     

Use of blast furnace granulated slag as a substrate in vertical flow reed beds: field application

Research was conducted at Middle East Technical University (METU), Ankara, Turkey in 2000 to determine whether a reed bed filled with an economical Turkish fill media that has high phosphorus (P) sorption capacity, could be implemented and operated successfully under field conditions. In batch-scale P-sorption experiments, the P-sorption capacity of the blast furnace granulated slag (BFGS) of KARDEMIR Iron and Steel Ltd., Co., Turkey, was found to be higher compared to other candidate filter materials due to its higher Ca content and porous structure. In this regard, a vertical subsurface flow constructed wetland (CW) (30 m(2)), planted with Phragmites australis was implemented at METU to treat primarily treated domestic wastewater, at a hydraulic rate of 100 mm d(-1), intermittently. The layers of the filtration media constituted of sand, BFGS, and gravel. According to the first year monitoring study, average influent and effluent total phosphorus (TP) concentrations were 6.61+/-1.78 mg L(-1) and 3.18+/-1.82 mg L(-1); respectively. After 12 months, slag samples were taken from the reed bed and P-extraction experiments were performed to elucidate the dominant P-retention mechanisms. Main pools for P-retention were the loosely-bounded and Ca-bounded P due to the material's basic conditions (average pH>7.7) and higher Ca content. This study indicated the potential use of the slag reed bed with higher P-removal capacity for secondary and tertiary treatment under the field conditions. However, the P-sorption isotherms obtained under the laboratory conditions could not be used favorably to determine the longevity of the reed bed in terms of P-retention.     

Anaerobic ammonium oxidation in constructed wetlands with bio-contact oxidation as pretreatment

Anaerobic ammonium oxidation (ANAMMOX) may provide an effective nitrogen removal pathway for constructed wetlands with low C/N influent. In a study of domestic sewage treatment, anaerobic ammonium oxidation process was identified in the pilot-scale constructed wetland of a bio-ecological process which was composed of a bio-contact oxidation reactor and a horizontal subsurface flow constructed wetland (CW). To investigate the ANAMMOX establishment in the bio-ecological process, two new CWs (planted and unplanted) were developed to be a control for the pre-existing CW. Under operational conditions of DO 2-3 mg/l, HRT 3.5 h for the bio-contact oxidation reactor, HRT 3 days for CWs, and domestic sewage as influent, the process achieved more than 90% TN removal rate after the ANAMMOX was established. The ANAMMOX bacteria on the media of the constructed wetlands were analyzed by specific polymerase chain reaction (PCR) with ANAMMOX specific primer set AMX818F-AMX1066R. The result of the genetic sequencing showed that the PCR product was related to Candidatus B. anammoxidans (AF375994.1) with 98% sequence similarity. Copy numbers of 16S rRNA gene of ANAMMOX bacteria in the pre-existing CW, the new planted CW and new unplanted CW were 3.47 × 10⁵, 3.02 × 10⁵ and 1.30 × 10⁵, respectively. These results demonstrated that the ANAMMOX process was successfully established and operated consistently in the constructed wetlands with a bio-contact oxidation reactor as a pretreatment, and that vegetation positively affected the growth and enrichment of ANAMMOX bacteria.     

Subsurface horizontal-flow constructed wetlands for wastewater treatment: The Czech experience

The first full-scale constructed wetland (CW) in the Czech Republic was built in 1989 and there are now three tertiary systems and 50 secondary treatment facilities. We report here on the design and operational efficiencies of these facilities. All CWs have been designed with horizontal subsurface flow. Coarse sand, gravel and crushed stones with size fraction of 4–16 mm are commonly used as substrates. The area of vegetated beds ranges between 18 and 4500 m² and operational CWs are designed for population equivalent (PE) of 4 to 1,100. Common reed (Phragmites australis) is the most frequently used macrophyte species.Results from systems studied during 1994 and 1995 show that the effluent concentrations of organics and suspended solids (SS) are well below the required discharge limits. In most cases the final effluent BOD₅ concentration is <10 mg l^–1. The relationship between vegetated bed BOD₅ inflow loadings (L ₀) and outflow loadings (L) is very strong (r=0.92). Constructed wetlands with subsurface horizontal flow usually do not remove larger amounts of nitrogen and phosphorus. The results from five Czech constructed wetlands show that nitrogen removal varies among systems, but the amount of removed nitrogen is very predictable. A regression equation between nitrogen inflow loading (L ₀) and outflow loading (L) produces a strong correlation (r=0.98). The most important process responsible for phosphorus removal in wetlands is precipitation with soil Ca, Fe and Al. However, the subsurface horizontal flow constructed wetlands use mostly coarse gravel and/or sandy materials and this provides little or no P precipitation. Results from monitored systems in the Czech Republic show that the percentage phosphorus removal varies widely among systems and is lower than the percentage removal of organics and suspended solids.     

A kinetic evaluation of anaerobic treatment of swine wastewater at two temperatures in a temperate climate zone

A static granular bed reactor (SGBR) was used to treat swine wastewater at 24 and 16 °C. At 24 °C, the organic loading rate (OLR) was 0.7-5.4 kg COD/m³ day and the average chemical oxygen demand (COD) removal efficiency was 88.5%, respectively. Meanwhile, at 16 °C, the OLR was 1.6-4.0 kg COD/m³ day and the average COD removal efficiency was 68.0%, respectively. The SGBR acted as a bioreactor as well as a biofilter. After backwashing, the recovery of COD removal was not a function of an OLR but recovery time, while that of TSS removal was not a function of either recovery time or the OLR. The maximum substrate utilization rate (k_max) ratio was 1.89 between 24 and 16 °C, and the half velocity constant (K_s) ratio was 1.22, and the maximum specific growth rate (μ_max) ratio was 4.71. In addition, the temperature-activity coefficient in this study was determined to be 1.09.