Accumulation of organic solids in gravel-bed constructed wetlands

1995 ◽  
Vol 32 (3) ◽  
pp. 229-239 ◽  
Author(s):  
Chris C. Tanner ◽  
James P. Sukias
Keyword(s):  
Organic Matter ◽  
Constructed Wetlands ◽  
Loading Rate ◽  
Dairy Farm ◽  
Effective Porosity ◽  
Water Losses ◽  
Gravel Bed ◽  
Tracer Dispersion ◽  
Conservative Tracer ◽  
The Impact

The effects of wastewater loading rate and planting with Schoenoplectus validus (soft-stem bulrush) on the accumulation of organic matter were investigated in four pairs of gravel-bed constructed wetlands. The planted and unplanted wetland pairs, each supplied with a different hydraulic loading of dairy farm wastewaters pre-treated in an anaerobic and aerobic lagoon, had received cumulative suspended solids loadings (∼ 82% volatile) of between ∼ 1.6 and 5.4 kg m−2 over a 22 month period. Vertical and horizontal gradients of organic matter accumulation were sampled by stratified coring, and the impact of solids accumulations on wastewater residence times investigated using bromide as a conservative tracer. Mean accumulations of organic matter in the unplanted wetlands ranged between 0.4 and 2.3 kg m−2, while those in the planted wetlands reached mean levels of nearly 4 kg m−2. Highest levels were recorded in influent zones (up to 9.5 kg m−2) and in the upper 100 mm of the substratum. The effective porosity of the highest loaded wetlands was markedly reduced compared to that in the lowest loaded wetlands, with mean retention times decreasing to around half of their theoretical values (corrected for evapotranspirational water losses). The planted wetlands retained higher apparent gravel porosity, despite greater accumulations of organic matter. High evapotranspiration rates during hot summer days, markedly extended retention times and increased tracer dispersion.

Treatment of Dairy Farm Wastewaters in Horizontal and Up-Flow Gravel-Bed Constructed Wetlands

1994 ◽  
Vol 29 (4) ◽  
pp. 85-93 ◽  
Author(s):  
Chris C. Tanner
Keyword(s):  
Constructed Wetlands ◽  
Retention Time ◽  
Loading Rate ◽  
Dairy Farm ◽  
Pilot Scale ◽  
Horizontal Flow ◽  
Loading Rates ◽  
Gravel Bed ◽  
Treatment Performance ◽  
Time Reduction

The treatment performance of four horizontal and two up-flow pilot-scale constructed wetlands planted with Schoenoplectus validus were investigated over a 20 month period (two winters and two summers) treating dairy parlour wastewaters at a range of loading rates. Removal of BOD.TN and TP were positively correlated with retention time. Reduction of BOD (70 - 90%) and SS (40 - 90%) in relation to loading rate were similar in both flow formats. The horizontal-flow wetlands showed 40 - 90 % reduction of TN and 30 - 80 % reduction of TP. The up-flow wetlands showed reduced levels of TN and TP removal, particularly when the loading rates were increased during the latter 5 months of the trial. Results are compared with those of other published studies of horizontal and upflow wetlands treating NH4-N rich organic wastewaters.

Functional role of earthworms to control the hydraulic conductivity of constructed wetlands 

2021 ◽  
Author(s):  
Océane Gilibert ◽  
Dan Tam Costa ◽  
Sabine Sauvage ◽  
Didier Orange ◽  
Yvan Capowiez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Hydraulic Conductivity ◽  
Constructed Wetlands ◽  
Hyporheic Zone ◽  
Riparian Zone ◽  
Water Flux ◽  
Sediment Surface ◽  
Deep Soil ◽  
The Impact ◽  
Organic Matter Input

<p>Wetlands are known for their natural service of water quality regulation. The hyporheic zones of the rivers filter and purify the surface water from the stream and infiltrated waters in soil nearby through the riparian zone. This purification service occurs because of a synergy between the substrate and its biodiversity (including plants, bacteria and other invertebrates). Our study deals with constructed wetlands (CW) as a nature-based solution mimicking wetlands water purification process, to purify wastewaters. The REUSE technology of CW is based on the use of specific layers of gravels and sands inside a close concrete structure, planted with specific sub-aquatic plants, where wastewaters or runoff of stormwaters are introduced to be filtered. The technology of Vertical Flow Constructed Wetlands (VFCW) reproduces the water flux observed in the riparian zone with a gravity flow of water. It is composed of reeds planted on a sandy layer (Ø 0-4 mm) and succession of gravel layers. This substrate can be saturated or unsaturated to reproduce the functioning of the hyporheic zone or the riparian zone respectively. By the time, the substrate is colonized by a community of bacteria producing biofilms which capture the residual organic matter from wastewaters to mineralize them. However, the VFCW substrates tend to clog over time due to the accumulation of organic matter and biofilms. Many studies consider earthworms as one of the solutions to alleviate this clogging, thanks to their burrows recreating macropores and preferential channels which help to improve the dispersion of water into the deep soil. The main goal of this study is to assess the impact of earthworm activities on the hydraulic conductivity of columns composed with the same substrate used in the VFCW. Different densities of earthworms (Eisenia fetida) were introduced (0, 100, 500, 1000 g of earthworms/m²) in these columns to be monitored for 37 days. The hydraulic conductivity was measured every 7 days, aside from day 23 with the addition of 40 g of peat bedding on column surfaces to simulate a high organic matter input. Columns with earthworm density superior to 500 g/m² shows an amelioration of their hydraulic conductivity after 21 days. These densities are also able to restore the hydraulic conductivity of the column in less than 7 days after the setting of clogged condition due to the organic matter input (peat bedding) at the sediment surface. This study showed that the burrowing activity of E. fetida improves the hydraulic flux of a sandy substrate and this impact is dependent on the earthworm density introduced. So, the addition of earthworms in the VFCW could serve as a prevention against clogging.</p>

Using Decomposition Kinetics to Model the Removal of Mine Water Pollutants in Constructed Wetlands

1994 ◽  
Vol 29 (4) ◽  
pp. 219-226 ◽  
Author(s):  
William J. Tarutis ◽  
Richard F. Unz
Keyword(s):  
Organic Matter ◽  
Constructed Wetlands ◽  
Mine Drainage ◽  
Term Treatment ◽  
Decomposition Kinetics ◽  
Dry Density ◽  
Organic Matter Concentration ◽  
Long Term Treatment ◽  
Input Variables ◽  
Reaction Stoichiometry

Although numerous mathematical models have been used to describe decomposition, few, if any, have been used to model the removal of pollutants in constructed wetlands. A steady-state model based on decomposition kinetics and reaction stoichiometry has been developed which simulates the removal of ferrous iron entering wetlands constructed for mine drainage treatment. Input variables for the model include organic matter concentration, reaction rate coefficient, porosity and dry density, and hydraulic detention time. Application of the model assumes complete anaerobic conditions within the entire substrate profile, constant temperature, no additional organic matter input, and subsurface flow only. For these ideal conditions, model simulations indicate that wetlands constructed with readily decomposable substrates rich in organic carbon are initially capable of removing far greater amounts of iron than wetlands built with less biodegradable substrates. However, after three to five years of operation this difference becomes negligible. For acceptable long-term treatment performance, therefore, periodic additions of decomposable organic matter will be required.

The impact of urban effluents on the coastal marine environment of Mediterranean islands

1995 ◽  
Vol 32 (9-10) ◽  
pp. 85-94 ◽  
Author(s):  
Michael O. Angelidis
Keyword(s):  
Heavy Metals ◽  
Organic Matter ◽  
Marine Environment ◽  
Suspended Particle ◽  
Pollution Source ◽  
Mediterranean Islands ◽  
Coastal Marine Environment ◽  
Coastal Marine ◽  
The Impact ◽  
The City

The impact of the urban effluents of Mytilene (Lesvos island, Greece) on the receiving coastal marine environment, was evaluated by studying the quality of the city effluents (BOD5, COD, SS, heavy metals) and the marine sediments (grain size, organic matter, heavy metals). It was found that the urban effluents of Mytilene contain high organic matter and suspended particle load because of septage discharge into the sewerage network. Furthermore, although the city does not host important industrial activity, its effluents contain appreciable metal load, which is mainly associated with the particulate phase. The city effluents are discharged into the coastal marine environment and their colloidal and particulate matter after flocculation settles to the bottom, where is incorporated into the sediments. Over the years, the accumulation of organic matter and metals into the harbour mud has created a non-point pollution source in the relatively non-polluted coastal marine environment of the island. Copper and Zn were the metals which presented the higher enrichment in the sediments of the inner harbour of Mytilene.

Fish farming in Denmark: environmental impact of regulative legislation

1995 ◽  
Vol 31 (10) ◽  
pp. 73-84 ◽  
Author(s):  
T. M. Iversen
Keyword(s):  
Organic Matter ◽  
Environmental Impact ◽  
Freshwater Fish ◽  
Aquatic Environment ◽  
Action Plan ◽  
Fish Farming ◽  
Fish Farms ◽  
Nitrogen And Phosphorus ◽  
Local Impact ◽  
The Impact

The main environmental problems associated with fish farming in Denmark are attributable to the dam, the “dead reach” and nutrient and organic matter discharge. The environmental regulation of fish farming in Denmark started with the Environmental Protection Act of 1974, the Statutory Order of 1985 forbidding wet feed, and the Action Plan on the Aquatic Environment of 1987. In the case of freshwater fish farms, the latter was implemented through the measures stipulated in the 1989 Statutory Order on Fish Farms. The impact of Danish legislative measures to reduce and regulate the environmental effects of freshwater fish farms can be summarized as follows: - the number of fish farms has been reduced from about 800 in 1974 to about 500 at present; - production has tripled since 1974 and has been stable since 1989; - a change from wet to dry feed has reduced the environmental impact of the farms; - the national goals of the Action Plan on the Aquatic Environment of 1987 for reducing fish farm discharges of organic matter, nitrogen and phosphorus have been fulfilled. The main remaining problems are that: - the local impact of fish farms on downstream stream quality is still much too high in about 15% of cases; - the problem of the passage of migrating invertebrates and fish is still unsolved at some farms; - the problems posed by “dead reaches” are still unsolved. It is concluded that sustainable fish farming is possible in Denmark, but with the present technology production will have to be significantly reduced.

Flow Pattern Analysis of Constructed Wetlands Treating Landfill Leachate

1999 ◽  
Vol 40 (3) ◽  
pp. 309-315 ◽  
Author(s):  
Jonathan K. Rash ◽  
Sarah K. Liehr
Keyword(s):  
Constructed Wetlands ◽  
Vertical Mixing ◽  
Subsurface Flow ◽  
Free Water ◽  
Chemical Reactor ◽  
Operating Conditions ◽  
Conservative Tracer ◽  
Residence Time Distributions ◽  
Physical Barriers ◽  
Interior Points

Three series of tracer studies were performed on three constructed wetlands at the New Hanover County Landfill near Wilmington, North Carolina, USA. One vegetated free water surface wetland (FWS-R), one vegetated subsurface flow wetland (SSF-R), and one unvegetated control subsurface flow wetland (SSF-C) were studied. A conservative tracer, lithium chloride, was used to study the chemical reactor behavior of these wetlands under normal operating conditions. Results indicated that short-circuiting is quite common in SSF wetlands, while FWS wetlands are well-mixed and not as subject to short-circuiting. These results were obtained from and reinforced with tracer measurements at interior points in these wetlands, analysis of residence time distributions from two different formulations, and the construction of residence volume distributions. The short-circuiting in the SSF wetlands can be attributed to the following: (1) Vertical mixing is inhibited by a combination of physical barriers and density gradients caused by rainfall and runoff dilution of the upper layer; and (2) Leachate is drawn from the bottom of the wetland, causing it to further prefer a flow path along the bottom.

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