Kenneth I. Ashley

Partial and full lift hypolimnetic aeration of medical lake, WA to improve water quality

Abstract Hypolimnetic aeration of Medical Lake, WA using partial lift and full lift aerator designs resulted in enhanced water quality. The partial lift system significantly reduced hypolimnetic ammonia (NH 3 ) and total phosphorus (TP) concentrations and increased hypolimnetic temperature. The system had no statistically significant effect on chlorophyll a (Chl a ) concentration, phytoplankton biovolume, hypolimnetic nitrate (NO − 3 ) and dissolved oxygen (DO) concentrations. The full lift system also significantly reduced hypolimnetic TP and NH 3 concentrations, but increased hypolimnetic DO and temperature. This system likewise had no effect on Chl a concentrations. Although anoxia persisted with the partial lift system, it was viewed as effective because phosphorus was not released from the lakes bottom, demonstrating that measurable concentrations of DO were not required to hold phosphorus in the sediments. Further research is required on (1) the effect of hypolimnetic aeration on stimulating DO depletion rates and (2) long term effects on phytoplankton biovolumes and Chl a concentrations. Continued operation of the full lift system should further reduce in situ oxygen demands and eventually a new equilibrium and higher hypolimnetic oxygen concentrations can be attained.

Hypolimnetic aeration: practical design and application

Abstract Hypolimnetic aeration is becoming increasingly important as a fisheries management and water quality improvement technique, however its application has been restricted by a paucity of practical reference material. Hypolimnetic aeration includes partial and full lift designs and several air/oxygen injection systems. Positive displacement compressors flanged to three phase electric motors are the preferred air supply and power for most lake aeration projects. Internal combustion power is adequate for short term use and wind power is in the developmental stage. Rubber compressed air hose is recommended for lake aeration applications. Free air delivery is the air volume taken into the compressor at standard temperature and pressure however actual output volume is regulated by discharge pressure. Performance specifications of full lift hypolimnetic aerators are based on water:air ratios, oxygen increase, transfer efficiencies and oxygenation capacity. An empirical sizing method is proposed using hypolimnetic volume, hypolimnetic oxygen consumption, water flow, air flow and inflow tube radius. Outflow tube radius should equal or exceed inflow tube radius to achieve high flow rates and allow efficient removal of residual bubbles. Floatation requirements are calculated from the total weight of the separator box, inflow and outflow tubes and the theoretical water head.

Factors influencing oxygen transfer in fine pore diffused aeration

A bench-scale experiment was conducted in a 701. tank of tap water to examine the effect of four design variables on oxygen transfer in a fine pore diffused aeration system. The experiment used non-steady state gas transfer methodology to examine the effect of air flow rate, air flow rate per diffuser, orifice diameter and reduced tank surface area on the overall oxygen transfer coefficient (KLa20, h−1); standard oxygen transfer rate (OT2, g O2 h−1); energy efficiency (Ep, g O2 kWh−1) and oxygen transfer efficiency (Eo, %). The experiments demonstrated that KLa20 and OTs increased with air flow rate (9.4–18.8 1 min−1) in the 40 and 140 μ diameter orifice range; however, Ep and E0 were not affected. Reducing the air flow rate per fine pore diffuser (40 and 140 μ diameter pore size) significantly increased KLa20, OTs, Ep and E0. A decrease in orifice diameter from 140 to 40 μ had no effect on KLa20, OTs, Ep and E0. A reduction in tank surface area had a marginally significant inverse effect on KLa20 and OTs, and no effect on Ep and Eo. The mean bubble size produced by the 40 and 140 μ diffusers was 4.0 and 4.2 mm, respectively. There was no consistent effect of air flow rate on bubble size within the range of air flow rates used in this experiment. In clean water aeration applications, the optimum system efficiency will be obtained using the largest number of fine pore diffusers operated at low air flow rates per diffuser. In wastewater treatment plants, higher air flow rates per diffuser should be used to prevent diffuser biofouling and keep biological solids in suspension. Wastewater systems are purposely operated at less than optimum transfer efficiencies in exchange for reduced diffuser maintenance and improved mixing. In either situation, changes in tank surface area and diffuser pore size (provided that pore diameter remains between 40 and 140 μ) are unlikely to have any significant effect on aeration system efficiency.

Hypolimnetic aeration: field test of the empirical sizing method

A hypolimnetic aeration system was recently installed in a small (16 ha Sα) eutrophic lake and a comparison made between measured performance and predicted performance from an empirical sizing method. The design variables used to size the system were: hypolimnetic volume 451,600 m3; maximum hypolimnetic oxygen consumption 0.2 mg l−1 d−1; aerator input rate 2 mg l−1; water velocity 0.76 m s−1 and depth of air release 12.2 m. A 3.7 kW compressor (0.57 m3 min−1) generated a water velocity of 0.46 m s−1, a water flow of 17.7 m3 min−1 and a theoretical hypolimnetic circulation period of 18 days. Dissolved oxygen increased by an average of 1.6 mg l−1 on each cycle through the aerator, and aerator input rates ranged from 0.6 to 2.6 mg l−1. Hypolimnetic oxygen consumption averaged 0.12 mg l−1 d−1 and ranged between 0.02 and 0.21 mg l−1 d−1. The aeration system was unable to meet the daily oxygen demand (90 kg) as the water velocity was slower than expected (0.46 m s−1). To avoid undersizing future aeration installations the following recommendations should be considered when using the empirical sizing formula: (1) estimates of oxygen consumption should be annual maximums from aerobic hypolimnia; (2) aerator input rates should be conservative (e.g. 1–4 mg l−1) and increase with depth; (3) water velocity of 0.45–0.50 m s−1 should initially be used when no information on actual bubble size or velocity is available; (4) aeration start-up should be timed to avoid periods of accumulated oxygen demands.

The Clear-water Paradox of Aquatic Ecosystem Restoration

Anders is a fi sheries scientist and an associate consultant with Cramer Fish Sciences and serves as affi liate faculty in the University of Idaho’s Department of Fish and Wildlife Resources in Moscow, Idaho. He can be reached at anders@fi shsciences.net. Ashley is a limnologist and environmental engineer with the Greater Vancouver Regional District and an adjunct professor in the Civil Engineering Department at the University of British Columbia, Vancouver.

Effects of orifice size and surface conditions on oxygen transfer in a bench scale diffused aeration system

Abstract Non‐steady state gas transfer methodology was used to examine the effect of orifice size and surface conditions on the rate of oxygen transfer in a 239 L bench scale tank. Each orifice size tested (40 μ, 397 μ and 1588 μ) increased the overall oxygen transfer coefficient (KLa20, hr−1) ; standard oxygen transfer rate (OTs, g O2/hr) ; transfer efficiency (Eo, %) and energy efficiency (Ep/ g O2/kW‐hr) as orifice diameter decreased. The three surface conditions examined exerted a minor effect on oxygen transfer.

International Conference on Nutrient Recovery from Wastewater Streams (Vancouver, 2009)

Closing the loop for nutrients in wastewaters (municipal sewage, animal wastes, food industry, commercial and other liquid waste streams) is a necessary, sustainable development objective, to reduce resource consumption and greenhouse gas emissions. Chemistry, engineering and process integration understanding are all developing quickly, as new processes are now coming online. A new “paradigm” is emerging, globally. Commercial marketing of recovered nutrients as “green fertilizers” or recycling of nutrients through biomass production to new outlets, such as bioenergy, is becoming more widespread. This exciting conference brings together various waste stream industries, regulators, researchers, process engineers and commercial managers, to develop a broad-based, intersectional understanding and joint projects for phosphorus and nitrogen recovery from wastewater streams, as well as reuse. Over 90 papers from over 30 different countries presented in this volume. ISBN: 9781843392323 (Print) ISBN: 9781780401805 (eBook)

Oxygenation performance of a laboratory-scale Speece Cone hypolimnetic aerator: preliminary assessment

A prototype laboratory-scale Speece Cone hypolimnetic aerator was used to examine the effect of oxygen in- put rate and outlet port water velocity on oxygen transfer, using four standard units of measure for quantifying oxygen transfer: (i) the oxygen transfer coefficient at 20 8C, KLa20 (h -1 ); (ii) the standard oxygen transfer rate (SOTR) (g O2� h -1 ); (iii) the standard aeration efficiency (SAE) (g O2 kWh -1 ); and (iv) the standard oxygen transfer efficiency (SOTE) (%). The maximum inlet velocity (i.e., 70 cms -1 ) was only 23% of the recommended design velocity (i.e., 305 cms -1 ), and the two-phase bubble swarm did not properly develop inside the cone, but remained as a gas pocket at the top of the cone, resulting in a drastically reduced bubble surface area to water ratio. Therefore, all of the performance measures from this prototype Speece Cone were much lower than would be expected with the recommended design inlet veloc- ity of 305 cms -1 . Despite this difference, the system was still capable of oxygen transfer efficiencies of about 61%, under low gas flow rates, which is still higher than any full-lift design hypolimnetic aerator operating on air. Future research efforts are focused on building a pilot-scale Speece Cone, with as close to the correct inlet and outlet veloc- ities, hydraulic residence time, and physical dimensions as possible, such that a two-phase bubble swarm could be generated. Once this experimental data is collected and analyzed, it can be properly compared with predictive models.

Water quality, chlorophyll, and periphyton responses to nutrient addition in the Kootenai River, Idaho

Abstract: During the past century, the Kootenai River, Idaho (USA), has experienced cultural oligotrophication following extensive levee construction, channelization, wetland drainage, and impoundment. A multiyear, whole-river nutrient-addition experiment was undertaken to mitigate these effects. The river was dosed with liquid agricultural-grade ammonium polyphosphate fertilizer (10-34-0) from June through September 2006–2010 to achieve an in-river total dissolved P (TDP) concentration of 3.0 µg/L. A fine-scale monitoring program included 8 sites over a 20-km reach (2 upstream control sites, one injection site, and 5 downstream treatment sites). Nutrient addition did not significantly increase N and P concentrations in the water column, but it significandy increased chlorophyll accrual rates and densities of edible green algae and diatoms. Nutrient addition significantly reduced NO3_+NO2_ concentrations, atomic TN:TP ratios, and densities of inedible cyanophytes. Mean NO3_ +NO2_ values decreased along a downstream gradient below the nutrient-addition site, whereas chlorophyll accrual rate typically peaked immediately downstream from the nutrient addition site then decreased progressively down-stream. Our study showed that nutrient addition is a useful river restoration technique for the Kootenai River.

Effects of Fertilization on Phytoplankton in Kootenay Lake, British Columbia

ABSTRACT Phytoplankton biomass, composition, and size structure were examined in oligotrophic Kootenay Lake, British Columbia, during two years of a fertilization program aimed at enhancing declining stocks of kokanee salmon. Phosphorus (47.1 metric tonnes per year) and nitrogen (206.7 metric tonnes per year) were added to the northern end of this long, narrow lake. Comparisons were made between the fertilized North Arm and unfertilized South Arm of the lake. The two arms did not indicate any significant differences in water chemistry prior to fertilization. Algal biomass was highest at the fertilized sites during the spring bloom (June) but did not differ between fertilized and unfertilized regions during the summer months (June 21 – September 21). There was an overall increase in biomass from 1992 (the first season of experimental nutrient loading) to 1993. Algal composition at the division level did not change between fertilized and unfertilized sites, except in 1993 when an increase in summer Chloroph...