Recirculation Period Research Articles

Biomechanics of abdominal aortic aneurysm in the framework of Windkessel effect and fully-developed inflow velocity via two-way non-linear FSI

Abdominal aortic aneurysm (AAA) is a pathological condition characterised by localised dilation of the infrarenal aorta, which can be fatal if rupture occurs. Current diagnostic criteria for repair are not patient-specific, but computational modelling may help to predict the potential growth and risk of AAA rupture accurately. This paper highlights how important using the Windkessel effect and fully-developed inflow velocity framework for the biomechanical analysis of AAA is; in other words, this research investigates how different boundary conditions in modelling methods affect the ability to correctly represent the biomechanics of AAA with complex non-linear parameters using a two-way fluid–structure interaction (FSI) technique. Time-averaged wall shear stress (TAWSS) is highly sensitive to boundary conditions, so unrealistic or simplified boundary conditions can lead to very different TAWSS results. This study also revealed that the use of outflow 3-element Windkessel boundary conditions on pulsatile pressure affects the flow pattern and increases the flow recirculation period. By accounting for the Windkessel effect and preventing backflow in numerical studies of AAA, the maximum displacement found in the distal branches can also be reduced. Models assuming plug velocity profiles overestimate peak wall stress by approximately 20% compared with models using fully developed parabolic inlet velocity profiles. This study incorporated a three-layer anisotropic material model and non-Newtonian fluid properties into the simulation, providing a more realistic representation of the effect of boundary condition selection on AAA mechanics. The results summarised from the parametric study could contribute to better prediction of AAA growth and rupture risk, and have important implications for the development of improved treatment strategies for AAA patients.

P52: ECMO Circuit Exchange on a Single Pump Console: Maximizing Mechanical Circulatory Support Resources in the High Census Pediatric Environment

Background: Pediatric hospitals have faced an unprecedented period of high census due to a confluence of respiratory illnesses, resulting in increased use of ECMO for rescue and long-term therapy. Combined with equipment demands imposed by a cardiac surgical program, ECMO disposables and pump console inventories have been stretched to their limits in many centers. Circuit exchanges place additional burden on device numbers, as two pump consoles are typically used for the changeout procedure. We report the case of an infant cardiac surgical patient requiring ECMO circuit exchange while the remainder of appropriately sized systems were in use on other patients in the hospital. Methods: A 3kg infant with complex congenital heart disease on VA ECMO post repair required circuit exchange due to consumptive coagulopathy and significantly increased trans-oxygenator gradient after multiple weeks of support. Due to a concurrent period of high ECMO utilization, a size appropriate replacement system was unavailable. In our institution, cardiac patients under 20kg requiring mechanical circulatory assistance are supported on a roller system with multiple pump heads, allowing conversion from ECMO to cardiopulmonary bypass without exposing the patient to an additional circuit and associated sequalae. After careful planning, the decision was made to build and prime a replacement circuit on the currently used pump base, using one of the accessory roller heads to de-air and recirculate the system. The pump-mounted oxygen tank was used to oxygenate the blood-primed circuit, and an extra heater was used to bring the perfusate up patient temperature. Three-way stopcocks placed on the venous, pre-, and post-oxygenator transducers allowed simultaneous pressure monitoring of both circuits. After a period of recirculation, the new infusion and return lines were handed up to the field and marked with white tape to denote new versus old tubing. A brief period off support was well tolerated as the circuits were changed out at the arterial and venous cannula connections, and subsequently the old circuit was removed from the pump base and discarded. Sweep control was re-established by the on-board mixer and flow meters, and water lines were reconnected to the on-board heater.

Sipekernik: Sistem Pemantau Kekeruhan Air dan Pengairan pada Akuaponik Menggunakan Sensor Turbidity, LDR dan Water Level

Aquaponics is an alternative to cultivating plants and fish in one place. This technique integrates fish farming with plants. In this case, aquaponic plants utilize nutrients from fish waste. Plants in aquaponics function as a biofilter, which will reduce these toxic substances into substances that are not harmful to fish and supply oxygen to fish-keeping ponds. With this technique, there will be a symbiosis of mutualism or a mutually beneficial cycle. The advantages obtained are the efficiency of water use and the reduction of waste contamination resulting from disposal into public waters. The water recirculation period affects the quality and quantity of fish and plants produced. Turbidity for cultivation should be no more than 25 NTU. Therefore, this tool is designed to detect the turbidity value of fish pond water in order to know the time to drain the pond using a turbidity sensor and regulate water irrigation in aquaponic installations based on light intensity values so that water does not stagnate in the installation pipe. The manufacture of this tool uses several components, such as an Arduino as a microcontroller, LDR (Light Dependent Resistor) sensor functions to turn on and off the pump, turbidity sensor functions to determine the turbidity value of pool water, and water level sensor functions to adjust the water level when draining and filling. pond water. At pump 1, the water will turn on if the intensity value of the LDR sensor is 650. If the turbidity sensor value is 25 NTU, then pump 2 will turn on and dump pool water into the shelter. After the pond water is drained to the specified height level, pump 3 will turn on to fill the fish pond with water. Pump 3 will stop when the water level is > 665.

Investigation of pulsed electric field operation as a chemical-free anti-scaling approach for electrodialysis desalination of brackish water

Pulsing the electric field is a strategy to mitigate concentration polarization in electrodialysis (ED). To evaluate the effects of the pulsed operation on the extent and kinetics of salt formation, a series of nine-day batch experiments were performed for pulsed and conventional ED (PED and CED, respectively). The pulsing duty cycle was set to 50 % and frequencies of 0.5 and 5 Hz were selected according to the divalent to monovalent ion fluxes calculated using the developed model. The results indicated that membrane scaling decreased in PED, with minimal scaling detected under 0.5 Hz. Concentration polarization moderation and lower supersaturation of the scale-forming ions in boundary layers as well as the removal of formed crystals from the stack during the pausing periods contributed to the reduction in scale formation. Considering that the scale-forming ions were transported to the concentrate channel within the first 50 % of the batch time, a novel hybrid pulsed-conventional operation was theorized that leveraged pulsing early in the batch and switched to constant voltage later to expedite the desalination process. Hybrid operation improved the desalination rate compared to a pure PED system and could potentially reduce membrane scaling by decreasing the recirculation period of the concentrate stream.

Removal of heavy metals in subsurface flow constructed wetlands: Application of effluent recirculation

This study reports four heavy metals, i.e., Zinc (Zn), Chromium (Cr), Nickel (Ni), and Lead (Pb) removal from landfill leachate employing two-hybrid subsurface flow constructed wetland systems; each system included a vertical flow (VF) followed by a horizontal flow (HF) wetland. The wetland systems were packed with organic (coco-peat) or construction (brick, sand) materials and planted with Phragmites australis or Chrysopogon zizanioides ( Vetiver ). Both systems were operated under without, and with effluent recirculation protocols. Cr, Ni, and Pb concentration were 2–73 mg/kg, 3–12 mg/kg, and 0.00004–27 mg/kg, respectively in Phragmites ; 8–34 mg/kg, 3–15 mg/kg, and 0.00004–14 mg/kg, respectively in Vetiver. Organic carbon (C) and iron (Fe) of the coco-peat, brick allowed media-based metals removal in VF wetlands; such accumulation was not quantified in sand-based HF wetlands. Zn, Cr, Ni, Pb removal percentages increased between 75 and 98%, 29 and 41%, 14 and 48%, 23 and 26%, respectively, in VF wetlands during the effluent recirculation period (compared with removal performances of without recirculation phase). Removal percentages were reduced in HF wetlands during the recirculation period. Overall, Zn, Cr, Ni, Pb removal percentages in the two-hybrid wetlands ranged between 20 and 97%, 95 and 99%, 55 and 73%, 69 and 83%, respectively.

Study of Biofilter Planted with Basil for Removal of Ammonia in Aquaponic Water

Abstract This experimental investigation of a laboratory scale aquaponic system included testing of a biofilter with basil plant as the biofilter part on aquaculture water quality. Irridescent shark was selected as aquaculture species. The biofilter consist of natural biomaterials such as coconut husk, coco peat, and coarse aggregates. The experiment was carried out for three short water recirculation durations of 2, 3, and 4 h/day. The influent and effluent ammonia NH3, total ammonia nitrogen (TAN), nitrites NO2 and nitrates NO3 levels were measured and analysed. The results showed that the biofilter effectively removed NH3 (65 - 71 %), TAN (34 - 58 %), and NO2 (60 - 67 %) from the aquaculture water. The dissolved oxygen (DO) levels were maintained between 3 - 7.0 mg/l during all the recirculation durations. The significance of water recirculation period was assessed by calculating the differences between the means of water quality parameters with a statistical test named one-way analysis of variance (ANNOVA) with significant level P taken as 5 %, i.e., P ≤ 0.5. The effluent mean NH3 levels 0.030 mg/l, 0.033 mg/l, and 0.022 mg/l exhibited significant difference at 4 h/d periods while effluent TAN levels 0.81, 0.77, and 0.77 showed no difference with varying periods.

Effect of effluent recirculation on nutrients and organics removal performance of hybrid constructed wetlands: Landfill leachate treatment

Landfill leachate treatment is challenging because of complex chemical composition. This study identifies the factors associated with organics and nutrients removal performance improvement in construction or organic materials based four hybrid wetland systems dosed with landfill leachate. The imbalanced pollutant composition ratio of leachate influenced removal pathways in the hybrid wetlands; effluent recirculation (50 and 25% ratios) adjusted leachate composition and improved removal performances. Mean nitrogen (N), phosphorus (P), biochemical oxygen demand (BOD), and chemical oxygen demand (COD) removal percentages in the hybrid wetlands during without, with recirculation periods ranged between 50 and 93, 69–100, 34–89, and 55–76%, respectively. Pollutant removals were achieved through adsorption, microbial (heterotrophic organic removal, ammonia assimilation, nitrification, denitrification) degradation, and plant uptake. Removal rates did not vary substantially among organic or construction materials based first stage VF (vertical flow) wetlands because of leachate composition. Constant water saturation depth variation influenced pollutant removal rates among the second stage wetlands. Shallow water depth HF (horizontal flow) wetlands appeared to be a promising wastewater treatment technology due to the coexistence of unsaturated, saturated bed matrix that supported diverse removal pathways.

Recovery of efficient treatment performance in a semi-aerobic aged refuse biofilter when treating landfill leachate: Washing action using domestic sewage.

Semi-aerobic aged refuse biofilters (SAARB) are known to efficiently remove organic matter, nitrogenous substances, and anions from landfill leachate. However, long-term recirculation of mature landfill leachate inevitably leads to accumulation of pollutants and decreases treatment capacity. In this study, the washing action provided by domestic sewage was used to recover and even enhance the treatment performance of SAARBs treating mature landfill leachate. Three SAARB columns were operated for 300d after which a "Recirculation-Washing-Recirculation" sequence was followed. In the first recirculation period (22d), removal of chemical oxygen demand (COD) and total nitrogen (TN) decreased from ca. 90% and 60%, respectively, initially to about 75% and less than 20%, respectively. Thereafter, washing (20d) of the SAARBs was accomplished by applying domestic sewage. In the subsequent second recirculation period (30d), the SAARBs were operated at the same hydraulic loading as used initially, but achieved high (ca. 90%) COD and relatively high (ca. 59%-76%) TN removal, including degradation of refractory organic matter such as humic- and fulvic-like substances. Overall, the mechanisms of the treatment performance recovery (including organics degradation and nitrification-denitrification) using domestic sewage can be attributed to three main effects: (1) some accumulated pollutants were washed out, thereby leading to recovery of the adsorption ability of aged refuse; (2) the inhibition of bio-refractory organics stress on microbial activities was mitigated by domestic sewage washing; and (3) the wash out of some accumulated salts (e.g., chloride and sulfate ions) probably helped the microbial activity recover.

Influence of the optical fiber deformations for a recirculation period in the optoelectronic perimeter security systems

Описан алгоритм работы подземной волоконно-оптической системы охраны периметра рециркуляционного типа с использованием WDM-технологии спектрального разделения информационных каналов. Представлены экспериментальные значения поперечных деформаций волоконного световода в зависимости от твердости пенополиуретанового упругого основания, количества точек деформации и массы идущего или ползущего нарушителя. Разработана математическая модель изменения временных интервалов между циркулирующими импульсами в зависимости от величины деформаций волоконного световода. Данная модель позволяет рассчитать величину дополнительных потерь в зависимости от радиуса изгиба, угла изгиба, вероятности туннелирования излучения из сердцевины в оболочку, параметров самого кварцевого волокна, а также от твердости упругой основы чувствительного элемента и количества точек деформации. Показано, что в случае постоянного радиуса деформирующего элемента R = 4 мм и одномодового ступенчатого волоконного световода для идущего нарушителя возникающие дополнительные временные задержки периода рециркуляции составляют 1,1–1,7 нс, для ползущего нарушителя данная величина находится в пределах 0,3– 0,9 нс.

A multi-functional and multi-compartment constructed wetland to support urban waterway restoration

Abstract This study assessed the significance of a multi-functional and multi-compartment constructed wetland (CW) implemented to restore a degraded urban waterway in Western Australia. The wetland was initially constructed as a surface flow system, then modified through the incorporation of the additional laterite-based subsurface flow system, with the potential for operation of a recirculation scheme and groundwater top-up during low water flows in summer. The CW performance was assessed by comparing nitrogen (N) and phosphorus (P) attenuation during base flow, high flow and episodic storm flow conditions. The performance varied from approximately 41% total nitrogen (TN) and 66% total phosphorus (TP) loads reduction during storm events, increasing up to 62% TN and 99% TP during low flow and summer recirculation periods. In overall, the CW attenuated about 45% TN and 65% TP loads from being delivered to the downstream sensitive river between 2009 and 2015. The CW design proved to be not only highly effective at reducing nutrient loads, but also improved the ecological services of the urban waterway by providing a diverse area for habitat and recreational activities.

Technique of Complete Heart Isolation with Continuous Cardiac Perfusion During Cardiopulmonary Bypass: New Opportunities for Gene Therapy

Cardiopulmonary bypass (CPB) featuring complete heart isolation and continuous cardiac perfusion is a very promising approach for solving the problem of efficient gene delivery. In the technique presented here, separate pumps are used for the systemic and cardiac circuits. This system permits continuous isolated arrested heart perfusion through optimizing a number of delivery parameters including temperature, flow rate, driving pressure, ionic composition, and exposure time to the cardiac vessels. During complete cardiac isolation, the blood vector concentration trended from 11.51 ± 1.73 log genome copies (GCs)/cm3 to 9.84 ± 1.65 log GC/cm3 (p > .05). Despite restructuring a very high concentration to the heart, GCs were detectable in the systemic circuit. These values over time were near negligible by comparison but detectable 1.66 ± .26 during 20 minutes of recirculation and did not change (p > .05). After the completion of the recirculation interval and subsequent washing procedure, the initial systemic blood vector GC concentration slightly increased to 2.08 ± .38 log GCs/cm3 (p > .05). During the recirculation period, we supported flow via the cardiac circuit around 300 mL/min. In this technique of heart isolation with continuous cardiac perfusion, >99% of the vector remains in coronary circulation during recirculation period. The animal’s non recirculation blood, or that in the system, was routinely tested during and after recirculation to contain much less than 1% of the original dose obtained via logging concentration of therapeutic over time. All of the sheep in this group recovered from anesthesia and received critical postoperative care, including all organ function, in the first 24–36 hours. Twenty-one sheep (84%) survived to euthanasia at 12 weeks. Average CPB time was 107 ± 19.0 minutes and cross-clamp time was 49 ± 7.9 minutes. This technology readily provides multiple pass recirculation of genes through the heart with minimal side effects of collateral expression of other organs.

Industrial wastewater treatment in constructed wetlands packed with construction materials and agricultural by-products

Abstract This paper reports pollutant removal performances from mixed industrial wastewater employing subsurface flow constructed wetland systems in Bangladesh. Two parallel hybrid wetland trains were established; each train included a vertical flow (VF) followed by a horizontal flow (HF) wetland. One hybrid system was packed with construction materials (i.e. recycled bricks), whereas the other system included agricultural by-products (i.e. sugarcane bagasse). All wetland units were planted with Canna indica. The hybrid trains were operated under non recirculation and recirculation phases; input hydraulic loading across each VF system ranged between 219.3 and 438.0 mm/d. Mean nitrogen, organics, solids, phosphorus and color removals across the hybrid systems were 67.5–80.0, 74.0–85.0, 55.0–95.0, 64.0–89.0 and 46.0–83.0% respectively. Lower input biodegradation ratio influenced organics removal routes in wetland systems that employed recycled bricks. In contrast, organic contents of sugarcane bagasse material supported microbial routes in the other system. VF wetland with organic media achieved higher TN removal rates (1.82 g/m2 d), due to internal carbon (C) generation. Higher phosphorus removals (89.0%) were observed in hybrid system packed with recycled brick media, due to adsorption process. HF wetland packed with recycled brick was efficient in removing color compounds, whereas the other HF system (with organic media) showed high sulfate removals. Nitrogen and BOD removal improvement was observed in VF wetland (packed with recycled brick media) during recirculation period; in contrast, effluent recirculation reduced removal rates of such pollutants in VF system that employed organic media. In general, this study shows potential application of particular materials as the main media of wetland systems, to achieve pollutant removals from industrial wastewaters in Bangladesh.

Origins of plateau formation in ion energy spectra under target normal sheath acceleration

Target normal sheath acceleration (TNSA) is a method employed in laser–matter interaction experiments to accelerate light ions (usually protons). Laser setups with durations of a few 10 fs and relatively low intensity contrasts observe plateau regions in their ion energy spectra when shooting on thin foil targets with thicknesses of the order of 10 μm. In this paper, we identify a mechanism which explains this phenomenon using one-dimensional particle-in-cell simulations. Fast electrons generated from the laser interaction recirculate back and forth through the target, giving rise to time-oscillating charge and current densities at the target backside. Periodic decreases in the electron density lead to transient disruptions of the TNSA sheath field: peaks in the ion spectra form as a result, which are then spread in energy from a modified potential driven by further electron recirculation. The ratio between the laser pulse duration and the recirculation period (dependent on the target thickness, including the portion of the pre-plasma which is denser than the critical density) determines if a plateau forms in the energy spectra.

The research on effect of purple soil enzyme activities by biogas slurry recirculation at large-scale farms

Soil enzyme plays an important role in converting soil nutrient, improving soil fertility and enhancing agricultural products quality. In this paper, the effect of purple soil enzyme activities was investigated by different biogas slurry (BS) recirculation load and period at large-scale farm in southwest China. The results indicated that the value of soil enzyme activities all increased by different BS recirculation load and period comparing to control check group. Its value was at high level by low BS recirculation load and long BS recirculation period. Soil urease and invertase activity reached highest value by T4 (7 m3·hm-2) and T8d (8 d), respectively. The value of soil catalase activity was highest by T1 (40 m3·hm-2) and T10d (10 d). In addition, soil phosphatase activity got peak value by T4 (7 m3·hm-2) and T4d (4 d). The effect of purple soil enzyme activities by BS recirculation at large-scale farms was explored to provide the theoretical basis for utilizing biogas slurry rationally.

Composition and sources of winter haze in the Bakken oil and gas extraction region

In the past decade increased use of hydraulic fracturing and horizontal drilling has dramatically expanded oil and gas production in the Bakken formation region. Long term monitoring sites have indicated an increase in wintertime aerosol nitrate and sulfate in this region from particulate matter (PM2.5) measurements collected between 2000 and 2010. No previous intensive air quality field campaign has been conducted in this region to assess impacts from oil and gas development on regional fine particle concentrations. The research presented here investigates wintertime PM2.5 concentrations and composition as part of the Bakken Air Quality Study (BAQS). Measurements from BAQS took place over two wintertime sampling periods at multiple sites in the United States portion of the Bakken formation and show regionally elevated episodes of PM2.5 during both study periods. Ammonium nitrate was a major contributor to haze episodes. Periods of air stagnation or recirculation were associated with rapid increases in PM2.5 concentrations. Volatile organic compound (VOC) signatures suggest that air masses during these episodes were dominated by emissions from the Bakken region itself. Formation rates of alkyl nitrates from alkanes revealed an air mass aging timescale of typically less than a day for periods with elevated PM2.5. A thermodynamic inorganic aerosol model (ISORROPIA) was used to investigate gas-particle partitioning and to examine the sensitivity of PM2.5 concentrations to aerosol precursor concentrations. Formation of ammonium nitrate, the dominant component, was most sensitive to ammonia concentrations during winter and to nitric acid concentrations during early spring when ammonia availability increases. The availability of excess ammonia suggests capacity for further ammonium nitrate formation if nitrogen oxide emissions increase in the future and lead to additional secondary formation of nitric acid.

Morphological features state of the blood supply and tissue viability in femoral and tibial bones during tourniquet limb ischemia and recirculation period

Detailed studies of histopathological changes and the state of blood supply to the tissues of the limb has not been studied yet. Application with following removing the tourniquet had not been carried out. It remains unclear topography, what are the most sensitive to ischemia parts of bone (bone and bone marrow), dynamics and pace of pathological and reparative changes.Objective: to establish experimental features of the blood supply, the viability and the possibility of tissue regeneration of the femur and tibia in the dynamics of ischemic and post-ischemic periods. Methods: we investigated the tissue of the femur and tibia in rabbits (of 76 limbs), in which created a tourniquet ischemia of the femur and tibia with varying duration (3 and 6 hours) followed by recirculation from 0.5 hours to 30 days. After sacrificing the animals ink-gelatin mass vascular injection performed with following histological analysis. Results: after the tourniquet application for 3 and 6 hours we found in the bone marrow of femoral and tibial epimetaphyses violations of the microcirculation in the sinusoids and small veins, which didn't result into ischemic necrosis. Such areas observed in the individual cases and in certain anatomical bone locations. Conclusions: in the tourniquet application on the hind limb of rabbits for 3 and 6 h,there are two different areas of circulatory disorders (compression and regional ischemia), in which tissues microcirculation and ischemic changes going off. After removing the tourniquet and blood supply recycling restoration different parts of the femur and tibia are differently sensitive to ischemia for tourniquet application for 6 hours were the primary structure of spongiosis and bone marrow of the proximal metaphyseal tibia.

Optimizing the in-line ozone injection and delivery strategy in a multistage pilot-scale greywater treatment system: System validation and cost-benefit analysis

Greywater is a potential source of recycled water for household that has often been overlooked. Although greywater is lightly contaminated, a holistic treatment and disinfection system of greywater is still warranted to ensure public health issues associated with the cross-connection of third pipe reticulation in household are minimized. This study assessed on the treatment performance of a commercial pilot-scale greywater treatment system comprising of a multi-medium sand filter, granulated activated carbon (GAC) filter and an ozonation disinfection system. The operational volume flow rate (10–20L/min) and ozone dosing rate (5–20g/h) for maximum removal of contaminants in greywater were investigated. This study found that the increase in operational volume flow rate decreased the overall performance of the greywater treatment and disinfection system. The optimum operating volume flow rate was found to be 10L/min, removing 72.6% of chemical oxygen demand (COD) and 42.9% (0.85-log removal) of Escherichia coli without recirculation. Recirculation of greywater was introduced to the ozonation disinfection system in order to improve the disinfection efficiency. It was found that all bacteria present in the treated greywater effluent were completely disinfected with a recirculation period of 1h.

Mineral and organic compounds in leachate from landfill with concentrate recirculation.

The effect of a reverse osmosis concentrate recirculation on the mineral and organic compounds in a landfill leachate was investigated. Investigated was the quality of a leachate from two landfills operated for different periods (a 20-year-old Cell A and a 1-year-old Cell B), where the concentrate was recirculated. Examined were general parameters (conductivity, pH), organic compounds (biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic nitrogen, BOD/COD), and inorganic compounds (nitrogen ammonia, sulfite, sulfate, cyanide, boron, chloride, ferrous, zinc, chrome, copper). The findings from the first year of investigation showed that over the initial period of recirculation, the concentration of organic compounds (BOD, COD) increased, but after 6 months their values stabilized. It indicates that the concentrate recirculation accelerated organic decomposition, especially in the new landfill Cell. The analysis of inorganic parameters showed that recirculation landfills produce a leachate with a higher concentration of N-NH4, and Cl(-). In case of the old landfill Cell, an increase in B and Fe was also noticeable. These compounds are cyclically washed out from a waste dump and require an additional pretreatment in order to exclude them from recirculation cycle. The increased concentration of Cu, Zn, and Fe was noticed during the initial months of recirculation and in the season of intense atmospheric precipitation in the leachate from both Cells. Higher values of electro conductivity, Cl(-), N-NH4 (+), B, and Fe in the leachate from the old field indicate that the attenuation capacity of this landfill is close to exhaustion.

Optimization of anaerobic fermentation of kitchen waste

Anaerobic fermentation is a suitable method of energetic and material utilisation of waste coming from restaurants and canteens. Laboratory experiments of wet anaerobic fermentation were performed in a continuous reactor and in batch reactors under mesophilic conditions. Effects of hydraulic retention time, organic loading rate, period of feeding and recirculation of digestate were examined in the continuous reactor. Effects of substrate pre-treatment (crushing, heating, freezing) were examined in the batch reactors. Degree of substrate degradation ranged between 83–85% within hydraulic retention time of 2–30 days. Appropriate organic loading rate was found in the range 2–3 kg of volatile solids per m3/day. Recirculation of digestate (both an inoculum for fresh substrate and replacement of fresh water supply) caused an increase in ammonia concentration and led to immediate inhibition of the process. The results further showed a positive effect of substrate pre-treatment in the initial phase of fermentation. However, degree of degradation did not show a significant increase for the period of 20 days of fermentation.    

Effect of recirculation on organic matter removal in a hybrid constructed wetland system

This research project aimed to determine the technologically feasible and applicable wastewater treatment systems which will be constructed to solve environmental problems caused by small communities in Turkey. Pilot-scale treatment of a small community's wastewater was performed over a period of more than 2 years in order to show applicability of these systems. The present study involves removal of organic matter and suspended solids in serially operated horizontal (HFCW) and vertical (VFCW) sub-surface flow constructed wetlands. The pilot-scale wetland was constructed downstream of anaerobic reactors at the campus of TUBITAK-MRC. Anaerobically pretreated wastewater was introduced into this hybrid two-stage sub-surface flow wetland system (TSCW). Wastewater was first introduced into the horizontal sub-surface flow system and then the vertical flow system before being discharged. Recirculation of the effluent was tested in the system. When the recirculation ratio was 100%, average removal efficiencies for TSCW were 91 +/- 4% for COD, 83 +/- 10% for BOD and 96 +/- 3% for suspended solids with average effluent concentrations of 9 +/- 5 mg/L COD, 6 +/- 3 mg/L BOD and 1 mg/L for suspended solids. Comparing non-recirculation and recirculation periods, the lowest effluent concentrations were obtained with a 100% recirculation ratio. The effluent concentrations met the Turkish regulations for discharge limits of COD, BOD and TSS in each case. The study showed that a hybrid constructed wetland system with recirculation is a very effective method of obtaining very low effluent organic matter and suspended solids concentrations downstream of anaerobic pretreatment of domestic wastewaters in small communities.