Effect of plant species on water quality at the outlet of a sludge treatment wetland

Sludge treatment wetlands are mainly used to reduce the volume of activated sludge, and the pollutants at the outlet are generally returned to the wastewater treatment plant. However, in cases where sludges are produced far from treatment plants not only must the sludge be treated, but the discharge of pollutants into the surrounding environment must also be limited. The aim of this study was to evaluate the efficiency of different plant species in optimising pollutant removal in a decentralised sludge treatment wetland. In addition, a new system design was assessed, in which the wetland was not completely drained, and a saturated layer was created using an overflow. The experimental setup consisted of 16 mesocosms in total, planted with monocultures of Phragmites australis, Typha angustifolia and Scirpus fluviatilis, and unplanted controls, each in four replicates.The experiment was conducted during the third summer of operation after setup. The system was fed with highly concentrated fish farm sludge at a load of 30 kg of total solids m⁻² yr⁻¹. Results showed that such wetlands were highly efficient, with removal rates between 94% and 99% for most pollutants. Planted systems generally outperformed the unplanted control, with a significantly lower mass of pollutants at the outlet of the sludge treatment wetland planted with Phragmites, followed by those with Typha and then Scirpus. The distinct influence of plant species on pollution removal was explained by the sequestration of nitrogen and phosphorus in plant tissues and by the rhizosphere effect, which enhance the biodegradation of organic matter, allowed the nitrification process and created redox conditions favourable to the sorption of phosphorus. Filtration and evapotranspiration rates played a major role in limiting the discharge of pollutants, and the impact was enhanced by the fact that the sludge treatment wetland was not completely drained.     

The humidity buffer capacity of clay–sand plaster filled with phytomass from treatment wetlands

The aim of our study was to measure the amount of moisture absorption and desorption in clay–sand plaster mixed with “fibre-wool” from Typha spadixes and chips of Typha and Phragmites. Common cattail (Typha latifolia) and common reed (Phragmites australis) are the most common plants in constructed and semi-natural wetlands for wastewater treatment, as they are highly valued in ecologically oriented construction. The cattail and reed for the experiment were harvested in a wastewater treatment subsurface flow semi-natural wetland and in two free water surface constructed wetlands which showed reliable aboveground phytomass production over a 5 years period (for Typha, 0.37–1.76 kg DW m⁻² in autumn and 0.33–1.38 kg DW m⁻², and for Phragmites, 0.61–1.32 and 0.61–1.02 kg DW m⁻², respectively). The quantity of moisture absorption and desorption was measured in a climatic chamber where the humidity of ambient air was suddenly raised from 50% to 80% (absorption) and reduced from 80% to 50% (desorption). Over 12 h, all of the samples released the same amount of water as they absorbed. The clay–sand plaster samples absorbed slower than they desorbed, whereas the gypsum wallboard required significantly more time for desorption. Added phytomass gave positive effects by reducing the weight of the clay–sand plaster, accelerating and increasing moisture absorption.     

Activated sludge treatment of abattoir wastewater—II : Influence of dissolved oxygen concentration

Performance of laboratory scale completely mixed activated sludge reactors fed with abattoir wastewater was measured at different dissolved oxygen (DO) concentrations. Degradation of fat present in the influent was inhibited at DO concentrations below about 0.5 mg l⁻¹, leading to sludges with high fat content which settled poorly due to excessive numbers of filamentous microorganisms. Fat was degraded rapidly at higher DO concentrations (up to 4.0 mg l⁻¹) and the sludge contained few filamentous microorganisms, a low fat content and settled readily. However, effluent quality was highest at low DO concentrations due to lower levels of soluble breakdown products from the fat.When wastewater was fed intermittently at constant aeration rate, sludge with a low fat content and good settleability resulted, even though the DO concentration was about 0.2 mg l⁻¹ for more than 30% of the time. Effluent quality was also high. Thus it is concluded that for full-scale abattoir treatment plants where wastewater flow is intermittent, DO concentration may be low during periods of high loading without adversely affecting effluent quality or sludge settleability.     

Removal of nitrogen, phosphorus and COD from waste water using sand filtration system with Phragmites Australis

The removal efficiencies of nitrogen, phosphorus and COD from waste water were examined using sand filtration systems with Phragmites australis (Cav.) Trin. ex. Steudel. The quality of effluent waters from the system with plant were far better than those from the one without plant, implying Phragmites could incorporate nitrogen and phosphorus into its tissues and promote phosphorus absorption onto the sand by the release of oxygen from the roots. The P-pot provided with the influent containing 198 mg l^- of total nitrogen and 21 mg l^-1 of total phosphorus had the highest biomass of Phragmites. Harvestable above-ground biomass accounted for about 3.5 kg m^-2 and removable nitrogen and phosphorus accounted for 69 and 6 g m^-2 respectively.The removal rates of total nitrogen and phosphorus in the system with Phragmites receiving variable amounts of COD were almost at the same level and also much better than those of the systems without plant, implying that the different COD concentrations in the influent media do not impair the removal efficiencies of nitrogen and phosphorus. Also Phragmites was found to resist COD concentration as high as 128 mg l^-1, and signs of clogging were not detected in this system throughout the experiment.     

Long-term effects of treated domestic wastewater on brown trout

A 12-month bioassay was conducted to determine the effects of unchlorinated, treated, domestic wastewater on survival, growth, swimming performance, and gill tissue of brown trout (Salmo trutta). Ammonia was the toxicant of concern, because the facility's effluent periodically exceeded the U.S. Environmental Protection Agency's (EPA) recommended criterion. Juvenile brown trout (initial weight = 2 g), which were exposed to six concentrations (0–37%) of effluent, were fed a restricted ration, so that growth rates were similar to those of wild stream residents. At the highest effluent concentration, monthly mean concentrations of un-ionized ammonia ranged from 0.004 to 0.055 mg l⁻¹ NH₃---N (at. wt = 14); these concentrations exceeded the EPA criterion of 0.016 mg l⁻¹ about 40% of the time. There were no significant effects of effluent concentration on survival, growth, or swimming performance of brown trout, but the degree of damage to gills was directly related to effluent concentration.     

An evaluation of the potential toxicity of treated bleached kraft mill effluent to striped bass (Morone saxatilis walbaum) larvae exposed through metamorphosis to the juvenile stage

Twenty-day-old striped bass (Morone saxatilis) larvae were exposed to a range of treated bleached kraft mill effluent (BKME) concentrations from 0 to 20% effluent by volume (v/v) under continuous flow test conditins. The experimental test concentrations in the 2–20% BKME test aquaria had a BOD₅ which ranged from < 1 to 5 mg l⁻¹, TSS 12–17 mg l⁻¹, and true color 35–416 mg l⁻¹. Bleached kraft mill effluent did not kill larvae exposed to it for 20 days through metamorphosis to the juvenile stage. The BKME did not alter growth in length, weight or condition factor in larvae over the 20-day exposure period as determined by multiple regression analysis. A linear regression analysis on the dry weight data at Day 20 only, however, indicated a trend of decreasing weight with increasing BKME concentration. Effluent-exposed larvae also developed normally during the 20-day study. All individuals examined completed the transformation from postlarvae to juveniles by the age of 40 days.     

Acute toxicity of unbleached kraft mill effluent (UKME) to the opossum shrimp, Neomysis americana smith

Ninety-six hour TL₅₀ values of unbleached kraft mill effluent (UKME) for Neomysis americana were found to range from concentrations of 3.29–6.85 per cent at 26–28°C and 3.90–7.30 per cent at 16–18°C. Differences between batches of effluent proved insignificant in experiments at each temperature regime. Furthermore, UKME did not lose its toxicity when stored for 5–7 days at 4°C. A concentration of 20 per cent effluent killed 100 per cent of the organisms in 8 of the 12 bioassays. Slope functions and confidence limits of TL₅₀ were calculated. Toxicity did not appear to be correlated with the Biochemical Oxygen Demand (BOD) of individual batches of raw effluent.     

Hydroponic tertiary treatment

Three macrophytes are found to grow well in trenches filled with a secondary effluent of a wastewater treatment plant in the absence of any support medium: Canna, Cyperus and Paspalum. Daily concentration changes of nutrients in the wastewater as well as evapotranspiration of the macrophytes were studied batchwise. After the vegetation had covered the trenches fully, the plants removed daily, 1.2–2.6 g of total nitrogen, 0.24–0.33 g of phosphate-phosphorus and 0.3–0.9 g of sulphate-sulphur per sq m. While ammonium and phosphate concentrations always decreased in water, sulphate was found to increase due to evapotranspiration. The daily water losses due to the latter was up to 20 l·m⁻² on sunny days. It was found that for extended nutrient removal under these conditions a hydroponic tertiary treatment plant could possibly produce no effluent at all. After harvesting, the aerial parts of the plant tissue contained comparable ash contents of 0.8–0.95% on wet base. Elementary analysis showed similar N and P contents of 23–26 g/kg and 2.3–3.8 g/kg respectively and differences in some inorganic elements of up to an order of magnitude between the three plants.     

Disruption of precopulatory behavior in the amphipod Anisogammarus pugettensis upon exposure to bleached kraft pulpmill effluent

Marine amphipods in precopula, Anisogammarus pugettensis (Dana), were used in static 117 h bioassays with neutralized, filtered, bleached kraft pulp mill effluent (BKME) and daily solution replacement. The effluent interfered with precopula behavior; high concentrations (40% of full strength BKME) resulted in rapid release of paired amphipods. A concentration-related time to 50% release of paired individuals was observed. For one batch of BKME, the behavioral threshold concentration (EC₅₀) was estimated at 10–15% of full strength BKME. The estimated 96 h LC₅₀ for underyearling coho salmon (Oncorhynchus kisutch) for the same effluent tested in freshwater was 36% BKME—illustrating a greater sensitivity of the amphipod behavioral bioassay in comparison to the salmonid acute lethal toxicity test. The amphipod precopula bioassay for toxicity testing has some merit in that it is moderately quantitative under given test conditions and does not require elaborate equipment.     

Use of photosynthetic bacteria for hydrogen sulfide removal from anaerobic waste treatment effluent

The feasibility of using photosynthetic bacteria to remove H₂S from anaerobic waste treatment effluent was investigated by growing fixed films of photosynthetic bacteria in a packed column or in a submerged tube system (“phototube”). Growth and enrichment for these organisms depended on constant illumination, anaerobic conditions and a substratum for attachment of the bacteria. Both systems were operated as flow-through processes using effluent from anaerobic (upflow) filters.Results showed that photosynthetic bacteria in fixed films can be effectively used for H₂S removal. Removal efficiencies of 81–95% were obtained on a 24-h retention time. Residual H₂S remained in the process effluent. The submerged “phototube”, showed dramatic improvement over the column, yielding a final effluent completely devoid of H₂S, at significantly shorter retention times and higher loading rates than the column. Performance appeared dependent on cell-H₂S contact and adequate illumination. The green photosynthetic sulfide-oxidizing bacterium, Chlorobium, was identified as a common organism in this phototube.This biological sulfide removal process offers the following advantages over currently used physical-chemical techniques: simplicity, no need for aeration or chemical additives and odor-free. Much research in process design is necessary before pilot or full scale application of the technique is possible.     

Role of aquatic plants in wastewater treatment by artificial wetlands

This report describes investigations using artificial wetlands which quantitatively assess the role of each of three higher aquatic plant types, Scirpus validus (bulrush), Phragmites communis (common reed) and Typha latifola (cattail), in the removal of nitrogen (via sequential nitrification-denitrification), BOD and TSS from primary municipal wastewaters. During the period August 1983–December 1984, the mean ammonia concentration of 24.7 mg l⁻¹ in the primary wastewater inflow (hydraulic application rate = 4.7 cm day⁻¹) was reduced to mean effluent levels of 1.4 mg l⁻¹ for the bulrush bed, 5.3 mg l⁻¹ for the reed bed and 17.7 mg l⁻¹ for the cattail bed, as compared to a mean value of 22.1 mg l⁻¹ for the unvegetated (control) bed. For all three vegetated beds, the mean effluent ammonia values were significantly below that for the unvegetated bed and for the inflow. The bulrushes and reeds (in that order) proved to be superior at removing ammonia, both with mean effluent levels significantly below that for the cattail bed. The high ammonia-N (and total N) removal efficiencies shown by the bulrush and reed beds are attributed to the ability of these plants to translocate O₂ from the shoots to the roots. The oxidized rhizosphere so formed stimulates sequential nitrification-denitrification. Similarly BOD removal efficiencies were highest in the bulrush and reed beds, both with mean effluent BOD levels (5.3 and 22.2 mg l⁻¹, respectively) significantly below that for the unvegetated bed (36.4 mg l⁻¹) and equal to or better than secondary treatment quality (30 mg l⁻¹). Our results demonstrate that higher aquatic plants can indeed play a significant role in secondary and advanced (N removal) wastewater treatment by wetland systems, a role that is completely distinct from that associated with their pollutant uptake capacity.     

Studies on the effects of sewage effluent on gastropod populations in experimental streams

Population density, biomass, growth and reproduction rate of the gastropods Lymnaea peregra (Müller) and Potamopyrgus jenkinsi (Smith) were monitored over a 21 month period in three experimental earth channels, one carrying clean river water and the others 25 and 50% treated sewage effluent mixed with river water. Each channel was divided into riffle and pool stretches; the abundance and biomass of both species were higher in the riffles. The abundance and biomass of L. peregra were significantly greater (P < 0.01) in the riffle in the presence of effluent. Concentration of effluent did not have a significant effect on abundance or biomass. The abundance and biomass of P. jenkinsi were significantly greater (P < 0.001) in riffle and pool in the absence of effluent. In addition, the abundance and biomass of P. jenkinsi were significantly greater (P < 0.05) in the 25% effluent channel than in 50% effluent. No significant differences in the growth of L. peregra between channels were observed. The average number of eggs and of egg masses laid by L. peregra was significantly greater (P < 0.01) in riffle and pool in the presence of effluent. In the riffle, significantly more masses (P < 0.05) and more eggs per adult (P < 0.01) were laid in the 25% effluent channel than in 50% effluent. No differences were observed in the reproduction rate per adult of P. jenkinsi between the 0 and 25% effluent channels. It is concluded that population differences between channels are probably largely the result of differing mortality rates.     

Algae removal by fine sand/silt filtration

A laboratory scale study was undertaken to determine the potential of a method of filtering algae from water using fine sand/silt as the filter media. Five median sand sizes (0.064–0.335 mm) and four bed depths (3.175–12.700 mm) were examined in constant head experiments with the algae Scenedesmus quadricauda. A total of 46 experiments were conducted with continuous measurements of filtration rate, head loss and effluent quality. All media with median sand sizes at or below 0.200 mm gave consistently high algae removal rates. The average removal was 97.27% (based on fluorescence) with a low average initial head loss across the filter media of 7.3 cm (median grain size diameter of 0.200 mm with the bed depth of 3.175 mm). Initial filtration rates obtained in the experimental apparatus were as high as 226 m³ m⁻²–day⁻¹ (3.84 gpm ft⁻²), comparable to conventional sand units. Run times were short due to surface clogging of the media. No chemical addition was required to obtain high removal levels.     

Liquid/suspended solid phase partitioning of polycyclic aromatic hydrocarbons in coal coking wastewaters

Wastewater samples were collected from five streams among two coke plants and characterized by high pressure liquid chromatography and gas chromatographic mass spectrometry. Wastewater streams included the ammonia still influent, ammonia still effluent and biological oxidation effluent. Samples collected from these streams were separated into liquid and suspended solid phases and each phase was analyzed for eleven polycyclic aromatic hydrocarbons (PAH). Total wastewater concentrations for these compounds ranged from about 2000 μg l⁻¹ in the ammonia still influent to 5–120 μg l⁻¹ in the biological oxidation effluent. Wastewater PAH were partitioned between liquid and suspended solid phases, and in most samples suspended solid phase PAH accounted for approx. 80% or more of total wastewater PAH. Partitioning in the biological oxidation effluent stream was correlated with aqueous solubility and n-octanol/water partition coefficients. Wastewater treatment consisting of sedimentation, ammonia stripping, and biological oxidation generally reduced liquid phase PAH concentrations to the range of 1 μg l⁻¹ or less. Effective removal of wastewater suspended solids will reduce total effluent PAH concentrations, hence there is need to address issues regarding removal of residual wastewater suspended material including characterization of the distribution of PAH with respect to suspended particle size.     

Effects of mixing velocity on anaerobic fixed film reactors

Four laboratory-model upflow anaerobic fixed film reactors (AFFR 1, 2, 3 and 4) treating landfill leachate were subject to identical volumetric organic load (7 kg COD m⁻³ d⁻¹) and hydraulic retention time (3d), but the contents in each unit were continuously recirculated for 10 months at four different velocities, respectively, of 21, 66, 680 and 3063 cm h⁻¹. The objective was to assess the effects of such mixing velocities (ν) on COD removal efficiencies (E), mean cell residence time (MCRT) and substrate utilization rate (U expressed as g COD removed d⁻¹ g⁻¹ VSS). The results showed that the relationships between E and ν and MCRT and ν were inverted U-shaped curves. The two middle reactors (AFFR 2 and 3) had near-optimum velocities (ν₂ and ν₃) with maximum E values of 88–89%. AFFR 4 had a high value of ν scouring biofilm on the biorings, resulting in higher concentrations of SS, VSS and COD in the effluent. All four reactors had nearly similar values of U (1.85–2.14 g COD d⁻¹ g⁻¹ VSS). The value of ν₁ (AFFR 1) was too low to enhance performance and ν₄ was too high to retain the biomass. The optimum recycle velocity, under the test conditions, was in the range of 66–680 cm h⁻¹.     

The effect of polysaccharidic gums on activated carbon treatment of textile wastewater

The activated carbon treatment of wastewater originating from the Celanese Canada Ltd., Carpet plant at Sorel, Quebec, was tested in this study. Typical plant effluent was characterized and prepared. Soluble organics in the synthetic effluent varied between 75–185 mg TOC 1⁻¹, consisting of dyes (10%) process chemicals (75%) and the soluble guar gum (15%) used as a viscosity adjusting additive in the newly installed continuous dyeing process.The activated carbon adsorption of the guar gum from its pure solution was examined in laboratory tests. Improved adsorption was observed at low pH values and at elevated adsorption temperatures. Lignite-based carbon out-performed bituminous coal-based carbon. At 30 mg TOC 1⁻¹ of soluble guar gum, low carbon loading in the range of 3–8 mg TOC g^–1 was recorded for various types of carbon at 20°C and neutral pH.Activated carbon adsorption of the typical conventional prepared dyehouse wastewater resulted in non-adsorbable residues in the range of 9–18 mg TOC 1⁻¹. Presence of 50–100 mg of polysaccharidic guar gum per liter of conventional wastewater mixture had a pronounced positive effect on the adsorption process. This is reflected in an increase in both the carbon loading at initial concentration and the adsorption isotherm slope.     

Removal of indigenous rotaviruses during primary settling and activated-sludge treatment of raw sewage

An eight month study of indigenous rotavirus removal during primary settling and activated sludge treatment of raw sewage was made in a plant in Houston, Texas treating 1.5 million gal day⁻¹. An average reduction of 44–55% was obtained by primary settling and a 93–99% reduction was achieved in final chlorinated effluents. Composite sampling at 1 h intervals over a 24 h period indicated average removals of 85% compared to a misleading 6% indicated by one set of grab samples of raw sewage and effluent collected simultaneously. Quantification of rotaviruses was made by immunofluorescent foci counts 24 h after addition of sample concentrates to coverslip cultures of fetal rhesus kidney cells. Rotaviruses varied from 40–5101⁻¹ of raw sewage and from 0 to 25 in the final chlorinated effluent.     

Taguchi approach for optimization of the bleeding on cement-based grouts

Investigations on the effect of the bentonite (B), fly ash (FA) and silica fume (SF) on the bleeding of cement-based grouts were reported here. Three additives (B, FA and SF) were used in the grout mixes to improve the bleeding of the grouts. Taguchi method was applied for the experiments and standard L₁₆ orthogonal array (OA) with three factors and four levels were chosen. In the preparation of the cement grouts, B, FA and SF were used at the ratios of 0–0.5–1–3%, 10–20–30–40% and 0–5–10–20%, respectively. The experiments were performed for three water/solid (W/S) ratios. Experimental results showed that the most effective material for the bleeding is SF. The bleeding decreased with the increase in SF and B ratio, while there was no noticeable difference with the increase of FA. Optimum conditions for minimum bleeding were obtained at 3% B, 10% FA and 20% SF for both grouts with W/S ratios of 0.75 and 1.0, while they were obtained 3% B, 20% FA and 20% SF for W/S ratio of 1.25. The Taguchi method was found to be promising tool to obtain the optimum conditions for such studies.     

Effect of pH on toxicity of kraft pulp and paper mill effluent to salmonid fish in fresh and seawater

In freshwater bioassays with juvenile rainbow trout (Salmo gairdneri), at initial pH values from 4 to 11, kraft mill effluents were considerably less toxic at pH 9–10 than at neutrality. When pH of test solutions was controlled throughout the bioassay period, the least toxic range was 8.5–9.5. Toxicity at typical receiving-water pH values was 50–67% greater.The acute toxicity of effluent samples to yearling coho salmon (Oncorhynchus kisutch) was identical for these effluents in seawater and freshwater respectively, provided that the pH was adjusted and held at the same value, and that test fish were previously acclimated to the dilution water for several months. Thus seawater constituents other than pH did not affect the acute toxicity of pulp and paper mill effluents appreciably.     

Growth responses of selected freshwater algae to trace elements and scrubber ash slurry generated by coal-fired power plants

In laboratory studies, the freshwater algae Ankistrodesmus falcatus, Scenedesmus obliquus, Selenastrum capricornutum, and Microcoleus vaginatus were exposed to potential pollutants from coal-fired power plants, and their growth responses were evaluated. Using a modification of the EPA Algal Assay Procedure Bottle Test, algae were incubated in media containing As(V) as Na₂HAsO₄ · 7H₂O, Cd(II) as CdSO₄, Hg(II) as HgSO₄, Se(VI) as Na₂SeO₄, in solution, and scrubber ash slurry generated at a western U.S. coal-fired power plant complex. First significant inhibition levels as well as algistatic-algicidal levels are reported. The median effective concentration (EC50) values for the potential pollutants ranged from 0.048–30.761 mg l⁻¹ (0.00064–0.41058 M) As(V), 0.005–0.019 mg l⁻¹ (0.00004–0.00017 M) Cd(II), 0.033–0.253 mg l⁻¹ (0.00016–0.00126 M) Hg(II), 0.033–8.511 mg l⁻¹ (0.00042–0.10779 M) Se(VI), and 3.048–15.417% scrubber ash slurry extract (SASE).