Heavy-metal uptake by crops from polluted river sediments covered by non-polluted topsoil

Cadmium uptake by maize from polluted river sediments covered with a clean top layer of variable thickness is discussed in relation to root distribution. Two pathways for uptake are distinguished: roots penetrating the contaminated layer or contaminants moving into the root zone. Relative Cd uptake proved to be roughly proportional to the fraction of total root length found in the contaminated layer. A deeper water table induced a deeper root development and more Cd uptake for a given thickness of clean topsoil. A model based on exponential decrease of root length density with depth is acceptable as first approximation only. Little or no evidence was found for contaminants moving into the root zone during the ten years of the experiment.     

Heavy-metal uptake by crops from polluted river sediments covered by non-polluted topsoil

Crop uptake of heavy metals from polluted river clay soils is shown to be reduced by covering the polluted soil with a layer of unpolluted clay soil. Plant experiments have been performed to determine the thickness of such a layer required either to comply with permissible levels for metal concentrations in foods and feeds, or to exclude any effect on plant metal levels. The experiments included cover layers up to 0.7 m and 1.6 m, respectively. Crops grown included cereals, potatoes, sugar beet, maize and various vegetables. Protection of all food crops tested against exceeding permissible levels for cadmium requires a clean topsoil of over 1.6 m; for individual crops ranging from zero (no cover layer required) for red cabbage, leek, onion, potato) to 1.2 m–1.6 m for celery tuber and leaf. Results for feed crops were variable: required topsoil depths for maize range from 0.25–1.2 m, and for wheat straw from 0.55 to 1.6 m. No-effect depths calculated for Cd, Cu and Zn demonstrate that inmany experiments the effect of the polluted soil may be observed at all topsoil depths tested. Heavy-metal concentrations in the soil profile, measured after completion of the experiments, showed no significant migration of metals from the polluted soil into the cover soil.     

Phosphorus removal by ponds receiving polluted water from non-point sources

Phosphorus discharged into the water column of lakes, streams, reservoirs, and ponds is either assimilated by algae or retained by the sediment. A laboratory study was conducted using intact sediment-water columns obtained from three ponds to measure their capacity to assimilate P. Phosphorus retention by these systems was determined at two P levels (2 and 10 mg PL^–1 or equivalent to an area loading of 26 and 130 g cm^–2). The potential P removal rates were 20.4, 28.8 and 30.8 g P CM^–2 day^–1 for PSF (pond adjacent to septic fields), PP(pond adjacent to a pasture), and PAF (pond adjacent to agricultural farm land), respectively. Longer residence time was needed for P removal at high P loading (10 mg PL^–1) than at low P loading (2 mg P L^–1). At high P loading, 76–82% of the floodwater P was removed within 10 days. All sediments showed a greater sorption capacity under reduced conditions than under oxidized conditions. At the P levels evaluated, pond sediments functioned as net sinks for water column P.     

Nitrogen removal enhanced by shunt distributing wastewater in a subsurface wastewater infiltration system

Three pilot subsurface wastewater infiltration systems filled with the same mixed matrix made of 80% brown soil and cinder at a weight of 20% were constructed in the laboratory. All systems worked successfully in the intermittent feeding mode with total hydraulic loading of 4 m³/(m² d) for over 2 months, with the optimal parameters of shunt ratio of 1:1 and shunt position at the depth of 0.7 m was achieved on the basis of large amounts of experimental data. The experiment results showed that shunt distributing wastewater could significantly improve the nitrogen removal in the subsurface infiltration system and the average removal rates of TN and NH₄-N increased by 10% and 5.67%, respectively. Shunt distributing wastewater had little influence on the removal rates of COD and TP. The results suggested that shunt distributing wastewater was simple and effective for nitrogen removal.     

Nutrient removal from polluted stream water by artificial aquatic food web system

For the removal of nutrients from eutrophic stream water polluted by non-point sources, an artificial aquatic food web (AAFW) system comprising processes of phytoplankton growth and Daphnia magna grazing was developed. The AAFW system was a continuous-flow system constructed with one storage basin of 3 m³ capacity, one phytoplankton tank of 3 m³ capacity, and one zooplankton growth chamber of 1.5 m³ capacity. The system was optimized by setting hydraulic retention time of phytoplankton tank as 3 days and D. magna density as 740–1000 individual l⁻¹. When the system was operated on eutrophic stream water that was delivering 471 g of total nitrogen (TN) and 29 g of total phosphorus (TP) loadings for 45 days, 250 g (53%) of TN and 16 g (54%) of TP were removed from the water during its passage through the phytoplankton tank. In addition, 64 g (14%) of TN and 4 g (13%) of TP were removed from the water by harvesting zooplankton biomass in the zooplankton growth chamber, resulting in significant overall removal rates of TN (69%), nitrate (78%), TP (73%), and dissolved inorganic phosphorus (94%). While the removal efficiency of the AAFW system is comparable to those of other ecotechnologies such as constructed wetlands, its operation is less limited by the availability of space or seasonal shift of temperature. Therefore, it was concluded that AAFW system is a highly efficient, flexible system for reducing nutrient levels in tributary streams and hence nutrient loading to large aquatic systems receiving the stream water. Handling editor: J. Padisak     

Nutrient removal in constructed microcosm wetlands for treating polluted river water in northern China

River water pollution is increasingly widespread in northern China and can lead to problems with the drinking water for the residents if not properly treated. Constructed wetlands are a promising solution and have become increasingly popular in China. In this study the nutrient removal and plant uptake in constructed microcosm wetlands vegetated with Typha orientalis, Phragmites australis, Scirpus validus and Iris pseudacorus for treating simulated polluted river water in northern China were investigated. The performance of the treatment systems from April to November was assessed. The maximum TN, NH₄-N and TP removal efficiencies were 68%, 93% and 67%, respectively. And the maximum nutrient uptake by plants constituted 51.89% of the N removal and 34.17% of the P removal throughout the trial. S. validus and I. pseudacorus have a higher nutrient uptake capacity and are preferred species from a treatment perspective in constructed wetland in northern China.     

Potassium removal accompanied by enhanced biological phosphate removal

The effects of potassium on excess uptake of phosphate in an aerobic-anaerobic activated sludge process were examined by the fill-and-draw procedure. The presence of sufficient potassium was necessary for excess uptake to occur. The contents of potassium and phosphate in the sludge at the end of each cycle of the process were correlated with each other by a non-linear equation, with some scattering. However, the sum of the molar ion valences of magnesium (Mg) and potassium (K), 2 Mg + K, was well correlated by a linear equation with the moles of P expressed as mmol/g-VSS, with a correlation coefficient of 0.993. When the potassium concentration was insufficient for the enhanced uptake of phosphate, its concentration in treated water was of the order of 0.1 mg/l. In the first anaerobic period phosphate was released into the liquid phase, but potassium was released after initial instantaneous removal, and in the successive aerobic period they were both taken up again.     

Nitrogen removal from animal waste treatment water by anammox enrichment

The aim of this work was to examine the applicability of the anaerobic ammonium oxidation (anammox) process to three kinds of low BOD/N ratio wastewaters from animal waste treatment processes in batch mode. A rapid decrease of NO(2)(-) and NH(4)(+) was observed during incubation with wastewaters from AS and UASB/trickling filter and their corresponding control artificial wastewaters. This nitrogen removal resulted from the anammox reaction, because the ratio of removed NO(2)(-) and NH(4)(+) was close to the theoretical ratio of the anammox reaction. Comparison of the inorganic nitrogen removal rate of the actual wastewater and that of control artificial wastewater showed that these two kinds of wastewater were very suitable for anammox treatment. Incubation with wastewater from RW did not show a clear anammox reaction; however, diluting it by half enabled the reaction, suggesting the presence of an inhibitory factor. This study showed that the three kinds of wastewater from animal waste treatment processes were suitable for anammox treatment.     

Denitrification by the sessile microbial community of a polluted river

Denitrification by the sessile microbial community of the River Tamagawa was studied in laboratory experiments. Inorganic nitrogen loss was observed when river water was incubated with sessile microbial community of the river in a continuously circulating system. It was confirmed by the ¹⁵N tracer technique that both sessile microbial communities of unpolluted and polluted areas had denitrifying activity, even though they were incubated in oxygenated river water. The denitrification rate of the sessile microbial community taken from a polluted area, measured by the ¹⁵N tracer technique, was 8–16 mg N/m²/day in October and December, 1977, and it was enhanced 10-fold by raising the water temperature from 14 to 30° C. Denitrification in the river was also suggested by determining the N₂: Ar ratio of gases evolved from the river bed.     

Vascular aquatic plants for mineral nutrient removal from polluted waters

Aquatic plants have potential as feedstuffs in certain nations, but the economics of harvesting and processing would prohibit their direct utilization as a forage in technologically advanced nations. However, nutrient pollution is accelerating rates of eutrophication of natural waters in many areas. Aquatic plants produce large standing crops and accumulate large amounts of nutrients. Systems based on the harvest of aquatic plants have potential application in removing nutrients from effluents and natural waters.     

Nitrogen and phosphorus removal rates using small algal turfs grown with dairy manure

Conservation and reuse of nitrogen (N) and phosphorus (P) from animalmanure is increasingly important as producers try to minimize transport ofthesenutrients from farms. An alternative to land spreading is to grow crops ofalgaeon the N and P present in the manure. The general goal of our research is toassess nutrient recovery from animal manure using attached algae. The specificobjective of this study was to evaluate the use of small subsections of algalturfs for determining N and P removal rates by attached algae under differentloading rates of dairy manure. Algae were grown in a laboratory–scalealgal turf scrubber (ATS) operated by recycling wastewater and adding manureeffluent daily. Replicate subsections (0.032 m²) ofalgal turf screens were removed and treated with five different loadings ofanaerobically digested dairy manure containing 5 to 80 mgL^–1 NH₄-N and 1 to 20 mgL^–1 PO₄-P over a 2-h incubationperiod. NH₄-N removal rates were biphasic with a fast initial ratefollowed by a slower rate. Biphasic rates were more pronounced for the lowestloading rates but less so for the higher ones. PO₄-P removal rateswere linear throughout the incubation period for all loading rates. N and Premoval rates increased with increasing loading rate and biomass. Inincubationsusing 1% dairy manure NH₄-N and PO₄-P removal ratesaveraged 0.72 and 0.33 g m^–2d^–1,respectively. These rates were approximately 5 to 8-fold lower than ratesmeasured on laboratory-scale ATS units using undisturbed turfs.     

Aerobic degradation of 3-chlorobenzoic acid by an indigenous strain isolated from a polluted river

An indigenous strain of Pseudomonas putida capable of degrading 3-chlorobenzoic acid as the sole carbon source was isolated from the Riachuelo, a polluted river in Buenos Aires. Aerobic biodegradation assays were performed using a 2-l microfermentor. Biodegradation was evaluated by spectrophotometry, chloride release, gas chromatography and microbial growth. Detoxification was evaluated by using Vibrio fischeri, Pseudokirchneriella subcapitata and Lactuca sativa as test organisms. The indigenous bacterial strain degrades 100 mg l⁻¹ 3-chlorobenzoic acid in 14 h with a removal efficiency of 92.0 and 86.1% expressed as compound and chemical oxygen demand removal, respectively. The strain was capable of degrading up to 1,000 mg of the compound l⁻¹. Toxicity was not detected at the end of the biodegradation process. Besides initial concentration, the effect of different factors, such as initial pH, initial inoculum, adaptation to the compound and presence of other substrates and toxic related compounds, was studied.     

Uranyl precipitation by biomass from an enhanced biological phosphorus removal reactor

Heavy metal and radionuclide contamination presents a significant environmental problem worldwide. Precipitation of heavy metals on membranes of cells that secrete phosphate has been shown to be an effective method of reducing the volume of these wastes, thus reducing the cost of disposal. A consortium of organisms, some of which secrete large quantities of phosphate, was enriched in a laboratory-scale sequencing batch reactor performing Enhanced Biological Phosphorus Removal, a treatment process widely used for removing phosphorus. Organisms collected after the aerobic phase of this process secreted phosphate and precipitated greater than 98% of the uranyl from a 1.5 mM uranyl nitrate solution when supplemented with an organic acid as a carbon source under anaerobic conditions. Transmission electron microscopy, energy dispersive x-ray spectroscopy, and fluorescence spectroscopy were used to identify the precipitate as membrane-associated uranyl phosphate, UO₂HPO₄.     

Investigation of microcystin removal from eutrophic surface water by aquatic vegetable bed

In southern China, many freshwater ecosystems, including lakes, rivers and reservoirs, are eutrophic. The nutrient loading coupled with year-round warm weather favors the growth of cyanobacteria, several of which can produce cyanotoxins, especially the potent liver toxins called microcystins, which are often detected in eutrophic drinking water sources. For purifying raw water used as source of drinking water treatment plants, an aquatic vegetable bed (AVB) experiment had been carried out in a hypertrophic waterfront of Lake Taihu, China, since October 2002. AVB was a simplification of the nutrient film technique (NFT) used to produce vegetables, which requires large quantities of water and nutrients. The average removal rates of total microcystin-RR and microcystin-LR were 63.0% and 66.7%, respectively. This study indicated that Ipomoea aquatica was able to absorb microcystins by using enzyme-linked immunosorbent assay (ELISA), and that the roots absorbed more toxins than leaves and stems. We used fluorescence in situ hybridization (FISH) to analyze the density of microcystin-degrading bacteria in AVB sediment. Two species of microcystin-degrading bacteria were detected, which indicated that microcystin bio-degradation processes did occur in AVB. Protozoa and metazoa were abundant in the rhizosphere. Aspidisca sp., Vorticella sp., Philodina sp., and Lecane sp. were the dominant species. The predation function of protozoa and metazoa had a positive effect on removal of cyanobacteria and microcystins.     

Nitrogen removal from secondary effluent by using integrated constructed wetland system

The treatment capacity of an integrated constructed wetland system (CWS) that was designed to reduce nitrogen (N) from secondary effluent was explored. The integrated CWS consisted of vertical-flow constructed wetland, floating bed and sand filter. The vertical-flow wetland was filled with gravel, steel slag and peat from the bottom to the top. Vetiver zizanioides was selected to grow in the vertical-flow constructed wetland and Coix lacrymajobi L. was grown in the floating bed. The results showed that the integrated CWS displayed superior removal efficiency for nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), and total nitrogen (TN). The average NO₃⁻-N, NO₂⁻-N, NH₄⁺-N and TN removal efficiencies of the integrated CWS were 98.83%, 95.60%, 98.05% and 92.41%, respectively, during the whole experimental operation. The integrated CWS may have a good potential for removing N from secondary effluent.     

Nitrogen removal from purified swine wastewater using biogas by semi-partitioned reactor

Nitrate and ammonium removal from purified swine wastewater using biogas and air was investigated in continuous reactor operation. A novel type of reactor, a semi-partitioned reactor (SPR), which enables a biological reaction using methane and oxygen in the water phase and discharges these unused gases separately, was operated with a varying gas supply rate. Successful removal of NO(3)(-) and NH(4)(+) was observed when biogas and air of 1L/min was supplied to an SPR of 9L water phase with a NO(2,3)(-)-N and NH(4)(+)-N removal rate of 0.10 g/L/day and 0.060 g/L/day, respectively. The original biogas contained an average of 77.2% methane, and the discharged biogas from the SPR contained an average of 76.9% of unused methane that was useable for energy like heat or electricity production. Methane was contained in the discharged air from the SPR at an average of 2.1%. When gas supply rates were raised to 2L/min and the nitrogen load was increased, NO(3)(-) concentration was decreased, but NO(2)(-) accumulated in the reactor and the NO(2,3)(-)-N and NH(4)(+)-N removal activity declined. To recover the activity, lowering of the nitrogen load and the gas supply rate was needed. This study shows that the SPR enables nitrogen removal from purified swine wastewater using biogas under limited gas supply condition.     

The use of periphyton communities for nutrient removal from polluted streams

The results of experiments on the efficiency of periphyton communities for nutrient removal from polluted streams in a continuous flow-through are given. The artifical stream (5 m × 0.7 m × 0.5 m) was made of wood, with silon (a kind of nylon) screens, as a substratum for periphyton growth. The elimination of nutrients was monitored by ammonium, nitrite, nitrate and orthophosphate analyses. In addition, the elimination of organics and the decrease in trophic state were determined. During two field experiments a marked elimination of nitrogen and phosphorus was demonstrated. The maximum efficiency of ammonium and orthophosphate removal was 80% and 70%, respectively. Organic removal reached 35% (C.O.D._Mn-Kubel) and 54% (B.O.D.₅). Inorganic and organic nutrient elimination caused significant changes in periphyton community structure in the outflow portion of the through, evaluated by the saprobic index and the similarity coefficient. The experiments confirmed that periphyton communities are a useful means of nutrient removal from polluted streams.