Short Hydraulic Residence Time Research Articles

Nutrient removal from sewage by an artificial food web system composed of phytoplankton and Daphnia magna

In order to remove nutrients from sewage, ecotechnology with an artificial food web composed of phytoplankton and Daphnia magna was used. To optimise performance of the system, phytoplankton growth, zooplankton growth, and a continuous-flow system were used. For phytoplankton growth, stirring was 6.7 times faster than the settling in growth rate of Scenedesmus. Zooplankton growth was not influenced by phytoplankton succession, and the specific production coefficient of D. magna was 110.4 mg Daphnia dry weight (DW) per mg chlorophyll a (Chl a). Results indicated that removal of nutrients was better in a long hydraulic residence time (HRT) system than in a system with short HRT. The optimum retention time was found to be 3 days for the phytoplankton chamber and 1.5 days for the subsequent D. magna chamber, respectively, with total retention time of the combined chambers being kept at 4.5 days. When a pilot plant was operated under these conditions, the removal rates of total nitrogen (TN) and total phosphorus (TP) were 68 and 56%, respectively. In the material budget of TN, 32% of inputs passed on to effluent, 39% to sludge, 27% to air and 2% to harvested Daphnia. For TP, 44% of inputs passed on to effluent, 51% to sludge and 4% to Daphnia.

Effect of dissolved oxygen concentration on sludge settleability.

This laboratory study presents a detailed evaluation of the effects of dissolved oxygen concentration and accumulation of storage polymers on sludge settleability in activated sludge systems with an aerobic selector. The oxygen and substrate availability regime were simulated in laboratory sequencing batch reactor systems. The experiments showed that low dissolved oxygen concentration (< or =1.1 mg O2 l(-1)) had a strong negative effect on sludge settleability, leading to the proliferation of filamentous bacteria (Thiothrix spp., Type 021N and Type 1851). This negative effect was stronger at high chemical oxygen demand loading rate. This indicates that a compartmentalised (plug flow) aerobic contact tank, designed at short hydraulic residence time to guarantee a strong substrate gradient, with low dissolved oxygen concentration, might be worse for sludge settleability than an "overdesigned" completely mixed contact tank. Contrary to the general hypothesis, the maximum specific acetate uptake rate, poly-beta-hydroxybutyrate production rate, and resistance to short starvation periods are similar in both poor- and well-settling sludge. The results of this study support our previous hypothesis on the importance of substrate gradients for the development of filamentous structures in biological flocs, from soluble organic substrate gradients to dissolved oxygen gradients in sludge flocs.

A temperate, tidal lake‐wetland complex 2. Water quality and implications for zooplankton community structure

Lakes Waihola and Waipori are shallow, coastal, tidal lakes that experience wind‐induced sediment resuspension, saline intrusions, and high inputs of nutrients. To determine the influence of externally‐driven, physical factors on spatial and temporal patterns of water quality in the two lakes, meteorological, hydrological, and water quality data were collected over 1 year. Multivariate analyses indicated that wind energy was driving the main water quality gradient in the lakes, which was primarily related to wind‐induced resuspension of lake sediments. The major, seasonally regulated, non‐tidal freshwater inflow was important in determining nutrient and salinity gradients in the lakes. The main nutrient inputs to the system were identified as the regulated, non‐tidal inflow (the upper Waipori River) and the tidal inflow (lower Waipori River). The impact of water quality gradients on zooplankton community structure in the lakes was assessed by canonical multivariate methods. Salinity gradients, caused by seasonal saltwater intrusions, were strongly related to zooplankton community structure in the lakes. Nutrient gradients (indicative of trophic state) were also related to zooplankton community structure. Although wind‐induced sediment resuspension had the largest impact on water quality in the lakes, it had little impact on the zooplankton community structure in either lake. The relationships between water quality and zooplankton community structure were confounded in Lake Waipori because of its very short hydraulic residence time (annual mean =1.9 days). Zooplankton community structure was resilient to short‐term changes in suspended particulate matter concentrations but not to seasonal changes in salinity. The results of this study support others which have shown impacts of even relatively small variations in salinity on the structure of zooplankton communities. This highlights the vulnerability of zooplankton communities in coastal lakes and wetlands to increasing salinity resulting from sea level rise and global climate change.

AN INTEGRATIVE APPROACH TOWARDS UNDERSTANDING ECOLOGICAL RESPONSES TO DAM REMOVAL: THE MANATAWNY CREEK STUDY1

ABSTRACT: Dam removal has been proposed as an effective method of river restoration, but few integrative studies have examined ecological responses to the removal of dams. In 1999, we initiated an interdisciplinary study to determine ecological responses to the removal of a 2 m high dam on lower Manatawny Creek in southeastern Pennsylvania. We used an integrative monitoring program to assess the physical, chemical, and biological responses to dam removal. Following removal in 2000, increased sediment transport has led to major changes in channel form in the former impoundment and downstream reaches. Water quality did not change markedly following removal, probably because of the impoundment's short hydraulic residence time (less than two hours at base flow) and infrequent temperature stratification. When the impoundment was converted to a free flowing reach, the composition of the benthic macroinvertebrate and fish assemblages in this portion of Manatawny Creek shifted dramatically from lentic to lotic taxa. Some fish species inhabiting the free flowing reach downstream from the dam were negatively affected by large scale sediment transport and habitat alteration following dam removal, but this appears to be a short term response. Based on our observations and experiences in this study, we provide a list of issues to evaluate when considering future dam removals.

Treatment of rainbow trout farm effluents in constructed wetland with emergent plants and subsurface horizontal water flow

The objective of this research was to investigate treatment of aquaculture effluents of flow-through systems in created wetlands. The constructed wetlands types used in this study were subsurface root zone systems with emergent plants and horizontal effluent soil percolation. Three 1.40×1.00×0.70 m ( L× W× H) root zone systems were filled with sands of 1–2 mm particle size and planted with 20 rooted shoots of reed per square meter ( Phragmites australis). Nutrient removal of rainbow trout ( Oncorhynchus mykiss) effluents flowing through the wetland was determined for hydraulic loading rates of 1, 3 and 5 l/min corresponding to very short hydraulic residence times (HRTs) of 7.5, 2.5 and 1.5 h, respectively. Inflowing nutrients were removed within every continuously flooded wetland. Total suspended solids (TSS) and chemical oxygen demand (COD) were reduced by 95.8–97.3% and 64.1–73.8%, respectively, and demonstrated no influence of HRT. Total phosphorus (TP) and total nitrogen (TN) removal rates varied from 49.0% to 68.5% and 20.6% to 41.8%, respectively, and were negatively correlated with HRTs. Effluent purification was best at HRT of 7.5 h, but sufficient removal rates were achieved for shorter HRTs.

The Effect of Outflow Depth on Phosphorus Retention in a Small,Hypertrophic Temperate Reservoirwith Short Hydraulic Residence Time

Stratification and phosphorus fluxes (input, output, sedimentation, and release from sediments) were studied in České údolí Reservoir (49°43′N, 13°21′E; V – 2.65 × 106 m3; A – 1.04 × 106 m2; zmax – 5.5 m; surface altitude – 314 m a.s.l.) during two summer stratification periods which differed in outlet operation and in hydraulic residence time (1997: surface outlets and 14 days; 1998: bottom outlets and 23 days). Use of bottom outlets resulted in weaker thermal stratification, a less pronounced oxygen deficit in the hypolimnion, and significantly lower P retention (17%) in comparison with surface discharge (42%). Factors apparently contributing to lower retention of P during the use of bottom outlets were: (i) faster flushing of the hypolimnion which intensified longitudinal transport of particles, (ii) more intense P release from sediments due to a lower concentration of nitrate in the water column and to more frequent contact of sediments in the shallows with water of pH >9. During both periods, phytoplankton production was limited only by light, not by nutrients. Phytoplankton biomass was comparable in both years despite some differences in vertical distribution.

Microfiltration-adsorption hybrid system in organics removal from water

A series of experiments was conducted with a Millipore flat plate microfiltration module modified to incorporate in-line powdered activated carbon (PAC) addition. In-line PAC was mixed continuously through a spiral mixing device for a predetermined time prior entering a membrane unit. The results showed that this system is excellent in removing fulvic acid (FA). This system provides to sufficient contact time for PAC to adsorb organics compared to the system with in-line adsorbent addition. More than 85% of FA was removed from water containing 8 mg/l of FA. To achieve this following conditions were used:.(i) a velocity gradient G (mixing intensity) of 160.4 s–1; (ii) a hydraulic residence time (mixing time) of 4 minutes; (iii) a PAC dose of 260 mg/l; and (iv) membrane pore size of 0.22 μm. In case of low FA concentration (e.g. 1.2 mg/l) in water, the removal efficiency was almost 100%. The removal efficiency also increased with the increase of mixing intensity and mixing time. The permeate flux slightly improved when a membrane of pore size 0.22 μm was used with shorter hydraulic residence time and lower PAC concentration. This paper presents a mathematical model developed based on surface diffusion. The model successfully predicted the performance of this hybrid system.

Modeling Biooxidation of Iron in Packed-Bed Reactor

Acid mine drainage (AMD) from active and abandoned mines continues to be an important source of water pollution in the US and around the world. AMD typically has high levels of acidity, sulfate, and metals. A model based on Monod kinetics and originally developed for use with rotating biological contactors was modified for use with a packed-bed column reactor. The reactor was filled with expanded polystyrene beads to immobilize chemolithotrophic bacteria and fed up to 570 mg L{sup {minus}1} ferrous iron [Fe(II)] in simulated acid mine drainage. A tracer study indicated changing behavior as a function of hydraulic residence time (HRT), with a transition from complete mix flow behavior to plug flow behavior as HRT decreased. The Fe(II) oxidation efficiency exceeded 95% until the HRT was reduced below 0.5 h. The reactor performance could be predicted with the model using estimates from the literature for {cflx u} and Y. The experimentally determined half-saturation constant K{sub s} was found to range from 5 to 12 mg L{sup {minus}1}. The maximum volumetric capacity constant R{sub max} was estimated to be {approximately}360 mg Fe(II)h{sup {minus}1} L{sup {minus}1} beads under complete mix flow conditions but appeared to be as high as 724 mg Fe(II)h{supmore » {minus}1} L{sup {minus}1} beads as conditions approached plug flow at short HRTs.« less

Relationship between landscape characteristics, history, and lakewater acidification in the Adirondack Mountains, New York

Interactions between acidic deposition and watershed characteristics were evaluated for a group of lakes in the Adirondack Mountains, New York. Landscape characteristics were compiled and examined relative to paleolimnological inferences of historical acidification. Results of estimates of acidification using the Model of Acidification of Groundwater in Catchments (MAGIC) and paleolimnological analysis were compared to physical, biological, and landscape change data, including such factors as watershed disturbance, logging, fire, and windthrow, to evaluate if inclusion of additional processes could improve model estimates. Results of bivariate and multivariate analysis confirmed that lakes that have experienced historical acidification tend to be those that receive relatively high amounts of precipitation and have short hydraulic residence times. These variables explained 58% of the diatom-inferred acidification. A combined model of long-term precipitation amount, hydraulic residence time, and recent blowdown accounted for 71% of the historic acidification in the Adirondacks. Lakes that have increased in pH since pre-industrial times tend to be those subject to substantial human disturbance and those that burned during major fires recorded after 1900. The magnitude of the discrepancy between MAGIC model and diatom-inferred hindcasts of acidification was not significantly correlated with any of the landscape change variables, suggesting that additional modifications to the MAGIC model to take into account landscape change are not likely to appreciably improve model performance.

Is the Sabine-Neches Estuary Net Heterotrophic or Autotrophic? A Reply to the Comment by Flinn et al.

In our earlier paper (Bianchi et al. 1997), we concluded that the Sabine-Neches estuary (southeast Texas) had low turnover of autochthonous carbon, based on low light penetrance, short hydraulic residence times (ca. 3 days), high inputs of refractory dissolved organic carbon (DOC), and low inputs of autochthonous carbon sources to sediments. High POC: chlorophyll a ratios (values > 1400) also indicated that allochthonous carbon inputs were a significant source to this light-limited estuary. Annual mean concentrations of chlorophyll a (3.0 ,ug 1-1) and particulate organic carbon (1.1 mg 1-1) in the water column were found to be considerably lower than other shallow estuarine systems. Only during a low inflow period in October 1993, did we observe considerably higher chlorophyll a concentrations in the lower estuary (ca. 16 ,Ig 1-1), which we attributed to injections of coastal waters. Since we did not measure parameters such as bacterial production and biomass as well as dissolved inorganic carbon (DIC), it was clearly not our objective to determine if the Sabine-Neches estuary was net heterotrophic or autotrophic. However, our characterization of the Sabine-Neches as a predominantly net heterotrophic

Phytoplankton biomass and productivity in two oligotrophic lakes of short hydraulic residence time

Phytoplankton biomass and productivity at two sites in the newly impounded Lake Dunstan and, upriver, in Lake Wakatipu (Frankton Arm) showed ranges throughout 1 year of 0.2–2.0 mg chlorophyll a m−3 and 0.9–6.0 mg C m−3 h−1 (maximum rate of carbon fixation). Peaks in phytoplankton abundance occurred in spring and summer in both lakes, but relationships of biomass and productivity vs light and nutrients differed between the lakes. In Lake Dunstan, P‐vs‐I parameters indicated that phytoplankton were photo‐acclimated to prevailing light conditions. In the Frankton Arm, P‐vs‐I parameters indicated that phytoplankton were poorly adapted to light conditions. Phytoplankton biomass and productivity were only depressed at the shortest observed hydraulic residence times (< 3 days). Phytoplankton biomass and productivity in Lake Dunstan were predicted from dissolved and particulate nitrogen concentrations and mean mixed‐layer light intensity. Annual mean chlorophyll a level was predicted satisfactorily using a published empirical model based on total phosphorus and inorganic suspended solids; a published deterministic model developed for reservoirs was tested and did not predict chlorophyll a concentrations accurately. The results are discussed in the context of the paradigm of trophic upsurge which is commonly observed in newly impounded reservoirs.

Distribution of rare earth elements in sediment cores of Sabine-Neches Estuary

Vertical profiles of several rare earth elements (REEs) were precisely measured in four dated sediment cores from the Sabine-Neches Estuary. From the extensive use of light rare earth elements (LREEs)—enriched zeolites during catalytic cracking process in nearby oil refineries, a significant enrichment of LREEs such as Lanthanum (La) was expected in sediment layers deposited in the estuary in the 1960s and 1970s. The measured concentrations of LREEs, and Fe normalized enrichment factors indicate that sediments are not enriched with light rare earth elements derived from effluents of oil refineries. The lack of strong enrichment of REEs and other trace metals and radionuclides are attributed to the strong binding of these constituents with dissolved organic matter found in high concentrations, and short hydraulic residence time, and/or due to the dilution of these metals by riverine soil particles.

Subsurface flow wetlands—A performance evaluation

This paper evaluates data collected by the authors as well as other individuals and agencies at operational subsurface flow constructed wetlands. The purpose of the evaluation was to identify the influence of hydraulic loading, organic loading, hydraulic residence time (HRT) on removal performance for biochemical oxygen demand (BOD), total suspended solids (TSS), nitrogen and phosphorus. The results indicate that BOD and TSS removal can be very effective at a relatively short HRT and that BOD removal exhibits a linear relationship with organic loading. Effective nitrogen removal requires a longer HRT and appears to be limited by the low oxygen availability in these systems. Phosphorus removal is also somewhat limited and ranges from 30 to 60 percent. Design models for these parameters are available or under development.

Degradation of Pentachlorophenol in Bench Scale Bioreactors Using the White Rot FungusPhanerochaete chrysosporium

Biodegradation of pentachlorophenol by the white rot fungus Phanerochaete chrysosporium was investigated in three bench scale bioreactors: mechanically mixed suspended bioreactor, upflow fixed-film bioreactor, and fluidized bed bioreactor. PCP disappearance was enhanced by increased ligninase activity in a mechanically mixed suspended bioreactor after initial adsorption onto the mycelium. Live fungal cultures were able to degrade PCP in the sorbed phase. PCP degradation data in the upflow fixed-film bioreactor was rapid and adequately explained with a quasi-first order steady state model with a rate constant of 0.071 L/g biomass-hr.In the fluidized bed bioreactor, effluent PCP concentration varied slightly at hydraulic residence times of 5 to 90 minutes. The steady state PCP degradation first order rate constant was 0.1 L/g biomass-hr. Effluent PCP concentration was related to its influent concentration at a 5 minute hydraulic retention time. The PCP removal efficiency was 37 to 72% and improved by increasing hydraulic retention time and decreasing influent PCP concentration. The fluidized bed bioreactor using P. chrysosporium shows considerable promise for the degradation of PCP. Degradation was effective under conditions of short hydraulic residence time and the process was stable in the face of large variations in influent conditions.

Degradation of morpholine in several biodegradation tests and in wastewater treatment plants

The biodegradation of morpholine was determined by several static biodegradation tests and in a laboratory-scale wastewater treatment plant which was operated with municipal wastewater. Morpholine proved to be readily biodegradable in the OECD screening test and inherently biodegradable in the Zahn-Wellens test exhibiting a final degradation level greater than 90 %. Nevertheless, an adaption period of 7 to 20 days was necessary before degradation occurred. In the wastewater treatment plant which was supplied with 5 mg/l morpholine the adaption period was 10 to 12 days and the final degradation level was also greater than 90 %. Due to the short hydraulic residence time of the treatment plant shock-loading of morpholine (35 mg/l morpholine) caused an increase of morpholine in the effluent. Furthermore, it could be shown by several toxicity tests (respiration acitivity, dehydrogenase activity, nitrification activity) that the biological activity of activated sludge was not inhibited even at high concentrations of morpholine.

Combined Artificial Wetland and High Rate Algal Pond for Wastewater Treatment and Protein Production

The potential to optimize wastewater utilization, whilst achieving satisfactory nutrient removal has been investigated through a simple system combining an Artificial Wetland with a High Rate Algal Pond (HRAP). Receiving septic sewage at a surface loading equivalent to 13.5 cm/day the Wetland achieved COD removals of 59.2%, NH4−N of 34,6%, PO4−P of 31.9% and SS of 78%. The HRAP selectively cultivated an easily harvestable filamentous green alga through a combination of short hydraulic residence times (&amp;lt; days), and microscreens as selectors over the effluent stream. Passage of the effluent through this stage permitted COD removal to increase to 79.4%, NH4−N to 82.8% and PO4−P to 54.1%, whilst generating a highly proteinaceous (42% by wt) biomass at a rate of approximately 50 tons/hectare/year. This paper discusses the performance of the pilot scale facility over a twelve month period, identifying biological and operational influences on the system, and the physiological mechanics by which the wastewater treatment is accomplished.

Longitudinal and temporal trends in the water chemistry of the North Branch of the Moose River

Surface water acidification is potentially a problem in regions with low ionic strength drainage waters. Atmospheric deposition of sulfuric acid has generally been implicated as the causative agent of this problem, although other sources of acidity may contribute. The Adirondack region of New York State is an area with “acid-sensitive” surface waters and an abundance of acidic lakes. The intent of this study was to evaluate the processes regulating the acid/base chemistry of a series of lakes draining a large heterogeneous watershed in the Adirondack region of New York. The study site, the North Branch of the Moose River, is heterogeneous in its soil and geological characteristics. This variability was reflected through differences in water chemistry that occurred within the basin. The northern headwaters generally drain subcatchments with shallow, acidic soils. The resulting water chemistry was acidic (equivalence of acidic anions exceeded equivalence of basic cations) with high concentrations of Al and dissolved organic carbon (DOC). As this water migrated through a large lake (Big Moose Lake) with a moderate hydrologic retention time (∼0.5 yr), considerable loss of DOC was evident. As acidic water was transported through the drainage area, it mixed with waters that were enriched in concentrations of basic cations from the eastern subbasins. As a result, there was a successive increase in the acid neutralizing capacity (ANC) and a decrease in Al concentrations as water migrated from the northern reaches to the outlet of the watershed. In addition to these general trends, short-term changes in water chemistry were evident. During low flow summer periods concentrations of basic cations were elevated, while concentrations of SO 4 2− and NO 3 − were relatively low. These conditions resulted in less acidic waters (higher ANC) with relatively low concentrations of Al. During high flow winter/spring conditions, elevated concentrations of SO 4 2− and NO 3 − were evident, while concentrations of basic cations were reduced resulting in low pH (low ANC) waters with high concentrations of Al. Variability in the processes regulating the pH buffering of waters was apparent through these short-term changes in water chemistry. In the northern subbasin short-term fluctuations in ANC were minimal because of the buffering of Al under low pH conditions. Seasonal changes in the ANC were more pronounced in the eastern subbasin because of the predominance of inorganic carbon buffering in the circumneutral pH waters. Lakes in the west-central Adirondacks have characteristically short hydraulic residence times and elevated nitric acid inputs. As a result these waters may be more susceptible to surface water acidification than other “acid-sensitive” lake districts in eastern North America. Given the apparent interregional differences, extrapolation of chemical trends in the Adirondacks to other areas may be tenuous.

Anaerobic fixed-film reactors treating carbohydrate wastewater

Anaerobic downflow stationary fixed-film reactors operated at 35°C, successfully treated synthetic (sucrose-based) wastewater of different concentrations at high organic loading rates and short hydraulic residence times. Waste stabilization was due to the high concentration of active biomass retained in the biofilm. Biofilm biomass concentration increased with organic loading rate reaching a maximum of 8.7 kg VFS m −3 of reactor volume (0.112 kg VFS m −2 support surface). The biofilm was found to be completely active and unaffected by diffusional limitations up to an average thickness of 2.6 mm.

Predicting concentration of total phosphorus and chlorophyll a in a lake with short hydraulic residence time

The relationship between total phosphorus and chlorophyll a concentration was determined for Skinner Lake, Indiana over an annual cycle in 1978–79. Total nitrogen:total phosphorus ratios in the epilimnion ranged from 19 to 220 suggesting a phosphorus-dependent algal yield in the epilimnion. Approximately 90% of annual TP loading reached the lake via streamflow, and 93% of this entered during snowmelt and spring-overturn periods. At that time incoming water flushed the lake 2.4 times. Atmospheric loading accounted for 1.4% of annual TP load. Internal hypolimnetic TP loading occurred during summer stratification. Mean [chl a] for the ice-free period was 15.15 mg m−3, within the range expected for eutrophic lakes.