Hydraulic Application Rate Research Articles

Remoção de matéria orgânica do esgoto em solo de wetland construído

RESUMO Nos sistemas wetlands construídos os meios suportes tradicionalmente utilizados são areia grossa, cascalho, pedregulho e brita. Nesta pesquisa, foi utilizado o solo natural (Latossolo Vermelho-Amarelo) misturado com areia média, plantado (wetlands construídos) com arroz irrigado (Oryza sativa L.) ou não (controles). O objetivo foi avaliar a remoção de DBO dos esgotos domésticos pelos processos de imobilização do carbono da biomassa microbiana e da respiração basal (atividade microbiana). Foram utilizados três sistemas operando com taxas de aplicação hidráulica de 4, 8 e 15 cm.d1. Cada sistema apresentava três unidades wetlands construídos e três controles, as quais eram alimentadas com esgotos para tratamento, por fluxo vertical em regime não saturado, nas segundas, quartas e sextas-feiras, ficando os outros dias em descanso para aeração do solo. Os resultados mostraram que os solos foram capazes de reduzir as concentrações de DBO afluentes significativamente, com eficiência de remoção variando entre 97 e 99%. A remoção se deu pela mineralização da matéria orgânica e seu acúmulo no solo. Durante o início da aplicação do esgoto, houve inicialmente uma redução nos teores de matéria orgânica nativa do solo que passaram a aumentar paulatinamente com a aplicação dos esgotos. A atividade dos microrganismos decompositores aumentou proporcionalmente à taxa de aplicação de esgoto, porém taxas elevadas indicaram uma tendência à inibição dessa atividade. Nos solos das unidades controles, houve menores perdas de CO2 para a atmosfera, indicando uma maior imobilização do carbono nos solos.

Batch versus continuous feeding strategies for pharmaceutical removal by subsurface flow constructed wetland

This study evaluated the effect of continuous and batch feeding on the removal of 8 pharmaceuticals (carbamazepine, naproxen, diclofenac, ibuprofen, caffeine, salicylic acid, ketoprofen and clofibric acid) from synthetic wastewater in mesocosm-scale constructed wetlands (CWs). Both loading modes were operated at hydraulic application rates of 5.6 cm day−1 and 2.8 cm day−1. Except for carbamazepine, clofibric acid and naproxen, removal in CWs was significantly (p < 0.05) enhanced under the batch versus continuous mode. For all compounds tested except naproxen, values for first-order decay constants (k) for drain and fill operation were higher than that for the continuous mode of operation. Correlation between the distribution coefficient (log Dow) and removal efficiencies of pharmaceutical compounds in the CWs, showed that pharmaceutical removal efficiency was significantly (p < 0.1) and inversely correlated with log Dow value, but not with log Kow value.

STUDY ON DECENTRALIZED DOMESTIC WASTEWATER TREATMENT BY CONSTRUCTED WETLAND VERTICAL - SUBSURFACE FLOW SYSTEM FOR SMALL COMMUNITIES

This research investigated the feasibility of using constructed wetland system with vertical - subsurface flow (VF-SFS) for treating the decentralized domestic wastewater for household and small community. The pilot studied on three beds included three macrophytes tested parallel reed, vetiver and bulrush with four different hydraulic application rates (176, 132, 88 and 44 mm/ day).This study was tested with six different parameters such as biochemical oxygen demand (BOD), total suspended solids (TSS), orthophosphate (PO43-), ionized ammonia (NH4+) and nitrate (NO3-) nitrogen and total coliform loadings. The removal rate of characteristic parameters was obtained: BOD5 96%, TSS 96.9%, N-NH4+ 60.5%, PO43- 47.6%, total coliform 97.7%, respectively. In particular, the highest removal efficiency was obtained in the bed with the longer hydraulic retention time. Simultaneously, there was no removal difference among 03 beds constructed wetland with 03 different plant species, significantly. Through the results of research, VF-SFS can be considered an appropriate treatment method for domestic wastewater; however the additional pre-treatments were necessary to remove grit, heavy solids and floating scum.

Modelling and evaluation of nitrogen removal performance in subsurface flow and free water surface constructed wetlands

With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasaköy biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.

Nitrogen and bacterial removal in constructed wetlands treating domestic waste water

The current study was carried out to compare the performances of two combined systems at pilot scale: the first one is composed of a vertical flow bed planted with Phragmites and a horizontal flow bed planted with Typha. The second combined system is an unplanted one. Each vertical flow bed, placed in the upstream of the horizontal flow bed is fed intermittently with a flow rate of 0.144 m 3 per day corresponding to an hydraulic application rate of a 0.24 m 3/m 2/day. Such parameters as Kjeldahl nitrogen, ammonia, and nitrate, nitrite, total and faecal coliform in the influent and effluent of the wetland system are examined, and their removal rates are determined. Nitrogen removal in planted system was greater than in unplanted one especially for nitrogen Kjeldahl (27 and 5%) and nitrogen ammonia (19 and 6%). Whereas, removal of nitrate-nitrite in planted system is less than in unplanted one (4 and 13%). However, bacterial removal in both planted and unplanted system was similar.

Role of Macrophyte Typha latifolia in a Constructed Wetland for Wastewater Treatment and Assessment of Its Potential as a Biomass Fuel

In the last decade, constructed wetlands have been gaining in popularity as a reduced cost and low maintenance technology for treating wastewater from small urbanised areas. In these wetlands at the same time that pollutant removal from wastewater occurs, great quantities of biomass are produced. As according to some authors, plants must be harvested for the most effective removal of pollutants, large amount of biomass would be available for different uses. Although different solutions have been proposed (to transform it into compost or feed supplements for animals), the biomass potential for fuel production has been neglected. Therefore, the objectives of this work were focused to the study of the suitability of the macrophyte Typha latifolia produced in a wetland as a fuel. Main goals were: (1) to assess the role of the macrophyte, in the removal of biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), nitrogen, phosphorous and pathogens from raw municipal wastewater; and (2) to determine the thermochemical characterisation of the biomass produced in order to examine the suitability of the biomass as a fuel. The constructed wetland consisted of two beds, of 40 m2 each with gravel as the supporting medium. The hydraulic application rate was 50 mm day−1. One of the beds was planted with cattail (Typha latifolia) and the other one was used as an unplanted control bed. With regard to wastewater treatment efficacy, the results obtained agree with the important role of macrophytes for maintaining the wetlands treatment capability, particularly for systems with high organic matter and ammonia-N content. Due to the high biomass yields obtained in the planted bed, and to the thermal behaviour of both cattail biomass and their ash, the utilisation of cattail biomass as fuel in thermochemical processes could be recommended.

Constructed Wetlands as a Sustainable Solution for Wastewater Treatment in Small Villages

With the aim of solving the wastewater treatment problem in small villages, treatment performance of a pilot-scale subsurface-flow constructed wetland (SFW) was evaluated for removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), total and faecal coliform and faecal streptococci bacteria from raw municipal wastewater. Studies of the composition and thermal behaviour of the harvested biomass were achieved in order to assess their possible utilisation as a fuel. Two different hydraulic application rates (150, and 75 mm day −1) and two macrophytes, cattail ( Typha sp.) and reed ( Phragmites sp.), were assayed. High levels of BOD, COD and TSS removal for all treatments were obtained. The best removals were obtained in those beds with the lowest hydraulic application rate. With regard to the type of plant, no significant differences were found between cattail and reed performance; however, cattails showed to be by far (almost a factor of 2) the greatest producer of biomass (22 t [d.m.] ha −1). Both cattails and reeds presented high heating values (17–20 MJ kg −1). According to these results, it can be concluded that the wetland system utilised in this research could be a suitable solution for raw wastewater as a stand-alone treatment, although a previous pre-treatment in order to remove grit, heavy solids and floatable materials would be necessary. Besides, the obtained biomass could be utilised as fuel in a small boiler for domestic uses.

Application of constructed wetlands for domestic wastewater treatment in an arid climate

The present study consists in assessing the efficiency of a constructed reed bed for domestic wastewater purification under an arid climate. The experimental system is made up of four beds differing in length (20, 30, 40 and 50 m) and planted with Phragmites australis. Raw domestic wastewater inflow through these beds is horizontal with a flow of 10 litres per second. Hydraulic application rate varies between 0,86 to 2,16 m3.m−2.day−1. The frequency of irrigation is weekly. The studied parameters are: the organic load (COD and TSS), nutrients (total Kjeldhal nitrogen: TKN, NH4, total phosphorus: TP, PO4) and the parasitical load (helminth eggs). Results shows that the constructed reed beds are efficient in reducing organic load (TSS: 58% to 67%; COD:48% to 62%) and parasitical load (Helminth eggs: 71% to 95%) in arid climates even with high hydraulic application rate. However, reduction of nutrient concentrations by the four beds is slight (TKN: 23 to 43%; NH4: 18 to 41%; TP: 5 to 17%; PO4: −9 to 13%). At the hot period (March to August), the reed beds seem to be more efficient in reducing organic load, nutrients and parasitical load. This period coincides with the reed's exponential growth phase. Moreover, the largest bed (50m in length) showed the best efficiency in the removal of nutrients (TKN: 53%; NH4: 61%; TP: 30%; PO4: 14%) and parasitical load (helminth eggs: 99%). This is due to its lowest application rate (0,86 m3.m−2.day−1).

Application of constructed wetlands for domestic wastewater treatment in an arid climate

The present study consists in assessing the efficiency of a constructed reed bed for domestic wastewater purification under an arid climate. The experimental system is made up of four beds differing in length (20, 30, 40 and 50 m) and planted with Phragmites australis. Raw domestic wastewater inflow through these beds is horizontal with a flow of 10 litres per second. Hydraulic application rate varies between 0,86 to 2,16 m3.m−2.day−1. The frequency of irrigation is weekly. The studied parameters are: the organic load (COD and TSS ), nutrients (total Kjeldhal nitrogen: TKN, NH4, total phosphorus: TP, PO4) and the parasitical load (helminth eggs).Results shows that the constructed reed beds are efficient in reducing organic load (TSS: 58% to 67%; COD:48% to 62%) and parasitical load (Helminth egg: 71% to 95%) in arid climates even with high hydraulic application rate. However, reduction of nutrient concentrations by the four beds is slight (TKN: 23 to 43%; NH4: 18 to 41%; TP: 5 to 17%; PO4: −9 to 13%). At the hot period (March to August), the reed beds seem to be more efficient in reducing organic load, nutrients and parasitical load. This period coincides with the reed's exponential growth phase. Moreover, the largest bed (50m in length) showed the best efficiency in the removal of nutrients (TKN: 53%; NH4: 61%; TP: 30%; P04: 14%) and parasitical load (helminth eggs: 99%). This is due to its lowest application rate (0,86 m3.m−2.day−1).

Oxygen Utilization of Trickling Filter Biofilms

In-situ oxygen consumption rate (OCR) observations for trickling filter biofilms under different hydraulic, substrate loading, and oxygen availability operating conditions are presented. OCRs were determined for sucrose- and dextrin-based synthetic feedstocks by growing biofilms on a 1.2-m deep section of 60° cross-flow media that was enclosed within a reactor vessel, sealing the reactor vessel to outside air entry, and observing the time rate of decrease in the reactor’s oxygen partial pressure. The results indicate that OCRs increased proportionately with increasing influent substrate concentrations for the 40 to 120 mg/L SCOD range, increased slightly or remained relatively constant with increasing influent substrate concentrations for the 120 to 200 mg/L SCOD range, increased slightly with increasing DO saturation condition for the 7.4 to 10.1 mg/L range, were affected by oxygen availability for influent substrate concentrations throughout the 70 to 175 mg/L SCOD range, increased with increasing hydraulic application rate from 2.4 to 4.9 m³/m²-h, and were slightly greater than predicted by currently acknowledged models. Other observations include the following measured OCRs were at least three times greater than those estimated from clean media oxygen-transfer testing; without liquid and feedstock application, biofilms consumed oxygen at 80–104% of their usual rate; and maximum biofilm oxygen consumption was ≈680 mg/m²-h.

Gravel Media Filtration as a Constructed Wetland Component for the Reduction of Suspended Solids from Maturation Pond Effluent

Experiments were carried out in a horizontal gravel media filter (GMF) with media size ranging from 5-40 mm. Such gravel-based, sub-surface flow units have been used in both planted and unplanted formats in a range of constructed wetland systems. This GMF was subjected to various hydraulic application rates ranging from 1 m3/(m2.d) to 36 m3/(m2.d) over a twc-year period. The range of suspended solids (SS) concentration was 2-36 mg/l and that of turbidity (NTU) was 3-44 during the experimental period. The average removal of suspended solids varied from 30-86%. It was observed that SS was reduced by a maximum of 86% at an application rate of 13m3/(m2.d), within the above noted SS range. An additional laboratory scale experiment was carried out with artificially grown algae in a vertical perspex tube of 190 mm inner diameter (I.D.) in upward flow condition. Results from the laboratory scale and pilot scale experiments are presented and discussed. The study demonstrates that a constructed wetland format with a subsurface flow and horizontal gravel media component could be used as an alternative method for reducing suspended solids from maturation pond effluent

Phosphorus removal from secondary-treated wastewater using overland flow

The removal of total phosphorus from secondary effluent by overland flow was studied using five terraces constructed 91 m in length and 140 or 70 m in width. Three methods of wastewater application were tested on the terraces including sprinkler, fan nozzle, and gated pipe. In addition, three different application rates were used. Samples of applied wastewater, runoff collected at points along the terraces, effluent from each terrace, and soils were analyzed for total phosphorus over a ten-month period. Hydraulic application rate had a significant effect on the removal of total phosphorus; the removal efficiency was inversely proportional to the hydraulic application rate. However, the method of application did not have an effect on phosphorus removal. An increase in phosphorus was observed in terrace soil samples; the increase was attributed to adsorption and precipitation.

Comparison between a Perforated Pipe and a Fixed Sprinkler System for Land Disposal of Treated Petrochemical Effluent

At SITEL – the integrated effluent treatment system of Pólo Petroquímico do Sul (South Petrochemical Complex, Triunfo, Brazil) – the tertiary-treated effluent is disposed of on land at an average hydraulic application rate of 140 m3/ha.day. Two subsystems have been installed in order to minimize the devastation of indigenous vegetation during the construction phase, aiming also at investigating the cheaper processes to be adopted when expansions become necessary. The first subsystem consists of a network of perforated PVC pipes which distribute the effluent over a forested area through an arrangement compatible with the local basin divides. It is fed by six submersible centrifugal pumps operating at moderate heads (ca. 30 m H2O). The second subsystem comprises high capacity rotating impact sprinklers fixed on hilltops covered predominantly by grasses. It is fed by two dry well centrifugal pumps operating at higher heads. The design criteria for both systems stem from a “zero runoff” legal requirement applicable within the limits of the 100 ha disposal site. The two subsystems are compared as regards technical aspects and economics. Removal efficiencies are presented. Capital and running costs related to pumping stations, mains, distribution networks, ancillary equipment and appurtenances, power consumption, maintenance, operation, materials etc. are compared and discussed. Functions and indexes that may prove useful in feasibility studies for similar systems are presented.

Fate of viruses in artificial wetlands.

Little is known about the ability of wetlands to remove disease-causing viruses from municipal wastewater. In this study we examined the survival of several indicators of viral pollution (indigenous F-specific bacteriophages, seeded MS2 bacteriophage, and seeded human poliovirus type 1) applied in primary municipal wastewater to artificial wetland ecosystems. Only about 1% of the indigenous F-specific RNA bacteriophages survived flow through the vegetated wetland beds at a 5-cm-day-1 hydraulic application rate during the period from June through December 1985. The total number of indigenous F-specific bacteriophages (F-specific RNA and F-specific DNA phages) was also reduced by about 99% by wetland treatment, with the mean inflow concentration over the period of an entire year reduced from 3,129 to 33 PFU ml-1 in the outflow of a vegetated bed and to 174 PFU ml-1 in the outflow of an unvegetated bed. Such superior treatment by the vegetated bed demonstrates the significant role of higher aquatic plants in the removal process. Seeded MS2 bacteriophage and seeded poliovirus were removed more efficiently than were the indigenous bacteriophages, with less than 0.2% of MS2 and 0.1% of the poliovirus surviving flow at the same hydraulic application rate. The decay rate (k) of MS2 in a stagnant wetlands (k = 0.012 to 0.028 h-1) was lower than that for flowing systems (k = 0.44 to 0.052 h-1), reflecting the enhanced capacity for filtration or adsorption of viruses by the root-substrate complex (and associated biofilm).(ABSTRACT TRUNCATED AT 250 WORDS)

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 O 2 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.

The effect of leaf shape on the deposition of spray droplets in rice

Paddy rice is usually sprayed with different types of conventional hydraulic nozzles and application rates. Spray droplets are more easily captured by the tip of rice leaves; this phenomenon was therefore studied with rice plants in a settling tower so that deposition of droplets occurred under controlled conditions. Further tests were carried out in rice fields by dirferent methods. The deposition rate was generally higher at the leaf tip compared with other parts, whether the leaf was vertical, pointing downwards at an angle of 60 degrees, horizontal or in a normal position. Similar results could be obtained if leaf-like water-sensitive paper strips were used instead of a natural rice leaf. The deposition and distribution pattern found on field rice leaves confirmed these results. Deposits on water-sensitive papers of different widths (2–25 mm) showed fewer droplets as the target width increased.

High-rate overland flow

Recommended loading rates for treating raw domestic wastewater by overland flow are 6.3–15 cm wk −1. Information provided in the literature yields little insight regarding the upper range of hydraulic loading rates that could be effectively treated by overland flow. Therefore, field investigations were conducted to evaluate the performance of the overland flow system at overland flow rates from 0.95 m 3 day −1 m −1 width of slope (13 cm wk −1 to 4.15 m 3 day −1 m −1 (57 cm wk −1). Preliminary treated municipal wastewater was pumped to overland flow slopes, each approx. 3.7 m wide and 36.5 m long. The slope of each plot was 2.5%. The cover crop consisted of a mixture of ryegrass, bluegrass and fescue grass. The plots were operated for 2 years at six different hydraulic loading rates. Effluent BOD 5 concentration averages varied from 6 to 11 mg l −1. The reduction of influent BOD 5 concentration ranged from 87 to 93%. Mean effluent suspended solids values were from 6 to 9 mg l −1 with reductions of influent concentrations of 91–95%. Hydraulic application rate had little effect on percent BOD 5 or suspended solids removal. Total phosphorus reductions were minimal at all hydraulic application rates due to limited soil water contact. Ammonia concentration in the effluent ranged from 1 mg l −1 NH 3-N at the 0.95 m 3 day −1 m −1 (13 cm wk −1) applied flow rate of 11.7 mg l −1 NH 3-N at the 4.15 m 3 day −1 m −1 (57 cm wk −1) loading rate. Ammonia and nitrogen reductions decreased as the applied flow rate increased. Consequently, lower overland flow rates are necessary for nitrogen removal. The use of high-rate overland flow could potentially reduce the land necessary for this form of land application, if nutrient removal was not a local concern.