Feasibility study of biogas upgrading coupled with nutrient removal from anaerobic effluents using microalgae-based processes

The present research was conducted to simultaneously optimize biogas upgrading and carbon and nutrient removal from centrates in a 180-L high-rate algal pond interconnected to an external CO₂ absorption unit. Different biogas and centrate supply strategies were assessed to increase biomass lipid content. Results showed 99 % CO₂ removal efficiencies from simulated biogas at liquid recirculation rates in the absorption column of 9.9 m³ m^?2 h^?1, concomitant with nitrogen and phosphorus removal efficiencies of 100 and 82 %, respectively, using a 1:70 diluted centrate at a hydraulic retention time of 7 days. The lipid content of the harvested algal–bacterial biomass remained low (2.9–11.2 %) regardless of the operational conditions, with no particular trend over time. The good settling characteristics of the algal–bacterial flocs resulted in harvesting efficiencies over 95 %, which represents a cost-effective alternative for algal biomass reutilization compared to conventional physical–chemical techniques. Finally, high microalgae biodiversity was found regardless of the operational conditions.     

PRODUCTION AND NUTRIENT REMOVAL BY PERIPHYTON GROWN UNDER DIFFERENT LOADING RATES OF ANAEROBICALLY DIGESTED FLUSHED DAIRY MANURE1

Growing algae to scrub nutrients from manure presents an alternative to the current practice of land application and provides utilizable algal biomass as an end product. The objective of this study was to assess algal growth, nutrient removal, and nitrification using higher light intensities and manure loading rates than in the previous experiments. Algal turfs, with periphyton mainly composed of green algal species, were grown under two light regimes (270 and 390 μmol photons·m^?2· s^?1) and anaerobically digested flushed dairy manure wastewater (ADFDMW) loading rates ranging from 0.8 to 3.7 g total N and 0.12 to 0.58 g total P·m^?2·d^?1. Filamentous cyanobacteria (Oscillatoria spp.) and diatoms (Navicula, Nitzschia, and Cyclotella sp.) partially replaced the filamentous green algae at relatively high ADFDMW loading rates and more prominently under low incident light. Mean algal production increased with loading rate and irradiance from 7.6±2.71 to 19.1±2.73 g dry weight· m^?2·d^?1. The N and P content of algal biomass generally increased with loading rate and ranged from 2.9%–7.3% and 0.5%–1.3% (by weight), respectively. Carbon content remained relatively constant at all loading rates (42%–47%). The maximum removal rates of N and P per unit algal biomass were 70 and 13 mg·g^?1 dry weight·m^?2·d^?1, respectively. Recovery of nutrients in harvested algal biomass accounted for about 31%–52% for N and 30%–59% for P. Recovery of P appeared to be uncoupled with N at higher loading rates, suggesting that algal potential for accumulation of P may have already been saturated. It appears that higher irradiance level enhancing algal growth was the overriding factor in controlling nitrification in the algal turf scrubber units.     

Development of an attached microalgal growth system for biofuel production

Algal biofuel production has gained a renewed interest in recent years but is still not economically feasible due to several limitations related to algal culture. The objective of this study is to explore a novel attached culture system for growing the alga Chlorella sp. as biodiesel feedstock, with dairy manure wastewater being used as growth medium. Among supporting materials tested for algal attachment, polystyrene foam led to a firm attachment, high biomass yield (25.65 g/m², dry basis), and high fatty acid yield (2.31 g/m²). The biomass attached on the supporting material surface was harvested by scraping; the residual colonies left on the surface served as inoculum for regrowth. The algae regrowth on the colony-established surface resulted in a higher biomass yield than that from the initial growth on fresh surface due to the downtime saved for initial algal attachment. The 10-day regrowth culture resulted in a high biodiesel production potential with a fatty acid methyl esters yield of 2.59 g/m² and a productivity of 0.26 g/m⁻² day⁻¹. The attached algal culture also removed 61–79% total nitrogen and 62–93% total phosphorus from dairy manure wastewater, depending on different culture conditions. The biomass harvested from the attached growth system (through scraping) had a water content of 93.75%, similar to that harvested from suspended culture system (through centrifugation). Collectively, the attached algal culture system with polystyrene foam as a supporting material demonstrated a good performance in terms of biomass yield, biodiesel production potential, ease to harvest biomass, and physical robustness for reuse.     

Regulation of algal biomass in a small lowland stream: field experiments on the role of invertebrate grazing, phosphorus and irradiance

1. Field experiments were undertaken in a small Danish lowland stream to study the role of invertebrate grazing, phosphorus concentration and irradiance in the regulation of benthic algal biomass on stones. 2. Algal biomass was regulated by invertebrate grazing. The gastropod Ancylus fluviatilis prevented algal biomass build up in early spring at a density of about 900 ind. m^–2, and reduced algal biomass to very low levels during the algal growth period at a density of about 6000 ind. m^–2. Grazing pressure therefore might regulate the magnitude of peak algal biomass in Gelbæk stream, a finding in agreement with earlier field observations. 3. As phosphorus enrichment to around 152 μg l^–1 during the period when irradiance was not limiting did not result in any further increase in algal biomass, it can be concluded that algal growth in spring was not controlled by phosphorus limitation. 4. Algal biomass development differed significantly in a shaded and in a non-shaded reach of the stream. Only very low algal biomass accumulation was evident in the shaded reach, while in the non-shaded reach an algal biomass peak of about 800 mg chlorophyll m^–2 was evident after 6 weeks of colonization. The shaded reach represented the light condition in Gelbæk stream after leaf proliferation of the overhead canopy and high bank vegetation. The findings therefore suggest that irradiance available to the algal community after shading from riparian vegetation prevents further algal biomass increase and hence determines the timing of peak algal biomass in the stream. 5. The irradiance experiment also suggests that if not regulated by invertebrate grazing or shading by an overhead canopy in the summer, then the magnitude of peak biomass in Gelbæk stream will be regulated by self-shading in the algal community. 6. These field experiments support theories, derived from laboratory experiments and field studies, that regulation of algal biomass is a complex interaction of top-down and bottom-up mechanisms.     

EFFECT OF LOADING RATES ON NITROGEN REMOVAL EFFICIENCY AND NITRIFICATION WITHIN ALGAL TURF SCRUBBERS

Kebede-Westhead, E.¹, Pizarro, C.¹, Mulbry, W.¹, & Wilkie, A. C.^{2 1}Agricultural Research Service, U.S.D.A., Beltsville, MD 20705-2350 USA; ² Soil and Water Science Department, University of Florida, Gainesville, FL 32611-0960, USA A potential alternative to land application of livestock manures for crop production is the production of algae to recover the nitrogen (N) and phosphorus (P) present in the manure. The specific objectives of these experiments were to test the effects of different loading rates of anaerobically digested dairy manure on nitrogen removal efficiency and nitrification within algal turf scrubbers (ATS). Laboratory-scale ATS units were operated by continuously recycling 220 l of wastewater and adding manure effluents daily. The algal turfs contained mixed indigenous assemblages of benthic algae. The most abundant genera were Ulothrix, Oedogonium, and Rhizoclonium. Weekly harvest of algal biomass, and wastewater samples were analysed for total Kjeldahl nitrogen (TKN), ammonium (NH₄-N), nitrate, and elemental composition. In previous experiments with loading rates of 0.6–0.96 g TN m^-2 d^-1, algal nitrogen accounted for 42–50 % of input NH₄-N. Nitrate production accounted for the bulk of remaining input NH₄-N. Lower loading rates (0.24 and 0.48 g TN m^-2 d^-1) tested here showed a higher removal rate where algal nitrogen accounted for 71% of input NH₄-N (56% of TN), and nitrate production was negligible. The disappearance of NH₄-N from wastewater in scrubbers measured over 4–5 hours showed initial rates of about 6 mg NH₄-N hr^-1 g^-1 DW algae, corresponding to 3.7 g NH₄-N d^-1 m^-2. This was followed by slightly lower rates, probably indicating limitation in carbon and/or micronutrients.     

The ecology of Lake Nakuru

Summary The major pathways of energy flow in Lake Nakuru (East Africa) are presented. The trophic structure of this equatorial alkaline-saline lake shows no predictable long term continuity. During the five years of this study it had a bloom of Spirulina platensis that persisted at least two years, it had periods with low algal densities and in addition it had various transitional phases with dramatic fluctuations of species composition and density.The Spirulina platensis bloom is characterized by a rich and almost unialgal bloom of the cyanophyte Spirulina platensis minor, with a mean biomass of 3,500 kJ m^-3 (20 kJ 1 g dry weight). Net photosynthetic rates were very high at depths with optimal light conditions (230 kJ m^-3 h^-1), but algal self-shading made integrated rates modest (45 kJ m^-3 24 h^-1) relative to the high biomass. Of the eight primary consumers only five species contributed significantly to the consumer biomass of 220 kJ m^-3: the flamingo Phoeniconaias minor, the cichlid fish Sarotherodon alcalicus grahami, the copepod Lovenula africana, the dipteran larva Leptochironomus deribae, and the rotifer Brachionus dimidiatus. Consumption rates were 50% of net photosynthetic rates, production rates 10%. Secondary consumers (90% being the pelican Pelecanus onocrotalus and the Greater Flamingo Phoenicopterus ruber) had a biomass of about 6.8 kJ m^-3. Pelicans consumed almost the whole fish production (7.5 metric tons wet weight/day).At low algal densities the lake had a more diverse algal population but a reduced mean biomass of 1,500 kJ m^-3 and mean net photosynthetic rates of 12 kJ m^-3 24 h^-1. Primary consumer species diversity and biomass were also reduced. Consumption rates sometimes exceeded primary production rates. Rotifers probably contributed 50% to total consumption and 75% to total secondary production but the estimates of their role is speculative as the relative contributions of algae, bacteria and detritus to rotifer consumption are not known. Transitional phases are characterized by rapidly changing abiotic and biotic conditions with algal breakdowns and sudden population peaks at all levels. Rotifers dominated secondary consumers, they contributed 25% to the total biomass of 380 kJ m^-3, 90% to the total consumption rate of 290 kJ m^-3d^-1 and 95% to the total production of 41 kJ m^-3d^-1.The discussion focusses on problems of measuring primary production in alkaline-saline lakes, and the control of producer and consumer densities. The difficulty in assessing the importance of bacteria and rotifers is emphasized. Also questions of ecological stability and efficiency are addressed. Finally, some recommendations for conservational policy are included.     

Seasonal productivity of a periphytic algal community for biofuel feedstock generation and nutrient treatment

Algal biomass is a promising feedstock for biofuel production. With a high lipid content and high rate of production, algae can produce more oil on less land than traditional bioenergy crops. Algal communities can also be used to remove nutrients from impacted waters. The purpose of this study was to demonstrate the ability of an algal turf scrubber (ATS)™ to facilitate the growth of periphytic algal communities for the production of biomass feedstock and the removal of nutrients from a local stream. A pilot-scale ATS was implemented in Springdale, AR, and operated over the course of a nine-month sampling period. System productivity over the nine-month operating time averaged 26 g m⁻² d⁻¹. Total phosphorus and total nitrogen removal averaged 48% and 13%, respectively. The system showed potential for biomass generation and nutrient removal across three seasons.     

Algal turf scrubber (ATS) floways on the Great Wicomico River,Chesapeake Bay: productivity,algal community structure,substrate and chemistry1

Two Algal Turf Scrubber (ATS) units were deployed on the Great Wicomico River (GWR) for 22 months to examine the role of substrate in increasing algal productivity and nutrient removal. The yearly mean productivity of flat ATS screens was 15.4 g · m^?2 · d^?1. This was elevated to 39.6 g · m^?2 · d^?1 with a three‐dimensional (3‐D) screen, and to 47.7 g · m^?2 · d^?1 by avoiding high summer harvest temperatures. These methods enhanced nutrient removal (N, P) in algal biomass by 3.5 times. Eighty‐six algal taxa (Ochrophyta [diatoms], Chlorophyta [green algae], and Cyan‐obacteria [blue–green algae]) self‐seeded from the GWR and demonstrated yearly cycling. Silica (SiO₂) content of the algal biomass ranged from 30% to 50% of total biomass; phosphorus, nitrogen, and carbon content of the total algal biomass ranged from 0.15% to 0.21%, 2.13% to 2.89%, and 20.0% to 25.7%, respectively. Carbohydrate content (at 10%–25% of AFDM) was dominated by glucose. Lipids (fatty acid methyl ester; FAMEs) ranged widely from 0.5% to 9% AFDM, with Omega‐3 fatty acids a consistent component. Mathematical modeling of algal produ‐ctivity as a function of temperature, light, and substrate showed a proportionality of 4:3:3, resp‐ectively. Under landscape ATS operation, substrate manipulation provides a considerable opportunity to increase ATS productivity, water quality amelioration, and biomass coproduction for fertilizers, fermentation energy, and omega‐3 products. Based on the 3‐D prod‐uctivity and algal chemical composition demonstrated, ATS systems used for nonpoint source water treat‐ment can produce ethanol (butanol) at 5.8× per unit area of corn, and biodiesel at 12.0× per unit area of soy beans (agricultural production US).     

Characterization of a microalga Chlorella sp. well adapted to highly concentrated municipal wastewater for nutrient removal and biodiesel production

The feasibility of growing Chlorella sp. in the centrate, a highly concentrated municipal wastewater stream generated from activated sludge thickening process, for simultaneous wastewater treatment and energy production was tested. The characteristics of algal growth, biodiesel production, wastewater nutrient removal and the viability of scale-up and the stability of continuous operation were examined. Two culture media, namely autoclaved centrate (AC) and raw centrate (RC) were used for comparison. The results showed that by the end of a 14-day batch culture, algae could remove ammonia, total nitrogen, total phosphorus, and chemical oxygen demand (COD) by 93.9%, 89.1%, 80.9%, and 90.8%, respectively from raw centrate, and the fatty acid methyl ester (FAME) content was 11.04% of dry biomass providing a biodiesel yield of 0.12 g-biodiesel/L-algae culture solution. The system could be successfully scaled up, and continuously operated at 50% daily harvesting rate, providing a net biomass productivity of 0.92 g-algae/(L day).     

Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production

Microbial fuel cells (MFCs) and membrane photobioreactors are two emerging technologies for simultaneous wastewater treatment and bioenergy production. In this study, those two technologies were coupled to form an integrated treatment system, whose performance was examined under different operating conditions. The coupled system could achieve 92–97 % removal of soluble chemical oxygen demand (SCOD) and nearly 100 % removal of ammonia. Extending the hydraulic retention time (HRT) of the membrane photobioreactor to 3.0 days improved the production of algal biomass from 44.4 ± 23.8 to 133.7 ± 12.9 mg L^?1 (based on the volume of the treated water). When the MFCs were operated in a loop mode, their effluent (which was the influent to the algal reactor) contained nitrate and had a high pH, leading to the decreased algal production in the membrane photobioreactor. Energy analysis showed that the energy consumption was mainly due to the recirculation of the anolyte and the catholyte in the MFCs and that decreasing the recirculation rates could significantly reduce energy consumption. The energy production was dominated by indirect electricity generation from algal biomass. The highest energy production of 0.205 kWh m^?3 was obtained with the highest algal biomass production, resulting in a theoretically positive energy balance of 0.033 kWh m^?3. Those results have demonstrated that the coupled system could be an alternative approach for energy-efficient wastewater treatment and using wastewater effluent for algal production.     

Abundance and primary production of filamentous green algae Zygogonium ericetorum in an extremely acid (pH 2.9) mining lake and its impact on alkalinity generation

1. In extremely acid mining lakes, benthic filamentous green algae (Zygnemataceae, Chlorophyta) thrive as effective competitors for limited carbon (C). These algae could supply C for microbial‐mediated benthic alkalinity generation. However, biomass, productivity and impact of the acidobiontic filamentous green algae at pH ≤3 have not previously been determined. 2. Periphytic filamentous green algae was mapped by harvesting their biomass from 85 1 × 1 m quadrats in mining lake Grünewalder Lauch. Zygogonium ericetorum colonised water depths between 1.6 and 10.5 m covering 88% of total area. Biomass peaked at 5–6 m depth. Total Zygogonium biomass amounted to 72.2 t dry weight for the whole lake (0.94 km²), which corresponds to 16.1 t C and the accumulation of primary production from 2.2 years. 3. Growth of Zygogonium is moderately N, C and extremely P deficient, and seriously stressed by high rates of Fe deposition during summer. Consequently, net primary production (NPP) of Zygogonium, calculated from measured photosynthesis versus irradiance characteristics and calculated underwater irradiance (0.13 g C m^?2 year^?1) and in situ oxygen measurements (7.8 g C m^?2 year^?1), corresponds to only 0.3% and 18.1% of pelagic NPP. 4. Neither pelagic nor benthic Zygogonium primary production can supply enough C for efficient acidity removal. However, at rates of benthic NPP in summer of 21.4 mg C m^?2 day^?1, Zygogonium contributed 26% of the C equivalents to remove acidity associated with ferric iron, contributing at least seasonally to efficient alkalinity generation.     

Treatment of swine manure effluent using freshwater algae: Production, nutrient recovery, and elemental composition of algal biomass at four effluent loading rates

Cultivating algae on nitrogen (N) and phosphorus (P) in animal manure effluents presents an alternative to the current practice of land application. The objective of this study was to determine how algal productivity, nutrient removal efficiency, and elemental composition of turf algae change in response to different loading rates of raw swine manure effluent. Algal biomass was harvested weekly from laboratory scale algal turf scrubber units using four manure effluent loading rates (0.24, 0.40, 0.62 and 1.2 L m⁻² d⁻¹) corresponding to daily loading rates of 0.3–1.4 g total N and 0.08–0.42 g total P. Mean algal productivity values increased from 7.1 g DW m⁻² d⁻¹ at the lowest loading rate (0.24 L m⁻² d⁻¹) to 9.4 g DW m⁻² d⁻¹ at the second loading rate (0.40 L m⁻² d⁻¹). At these loading rates, algal N and P accounted for> 90% of input N and 68–76% of input P, respectively. However, at higher loading rates algal productivity did not increase and was unstable at the highest loading rate. Mean N and P contents in the dried biomass increased 1.5 to 2.0-fold with increasing loading rate up to maximums of 5.7% N and 1.8% P at 1.2 L m⁻² d⁻¹. Biomass concentrations of Al, Ca, Cd, Fe, K, Mg, Mn, Mo, Si, and Zn increased 1.2 to 2.6-fold over the 5-fold range of loading rate. Biomass concentrations of Cd, K, Pb, and Si did not increase significantly with loading rate. At the loading rate of 0.40 L m⁻² d⁻¹ (corresponding to peak productivity) the mean concentrations of individual components in the algal biomass were (in mg kg⁻¹): 250 (Al), 4900 (Ca), 0.30 (Cd), 1050 (Fe), 3.4 (Pb), 2500 (Mg), 105 (Mn), 6.0 (Mo), 7,500 (K), and 510 (Zn). At these concentrations, heavy metals in the algal biomass would not be expected to reduce its value as a soil or feed amendment.     

Hectare-scale demonstration of high rate algal ponds for enhanced wastewater treatment and biofuel production

High rate algal ponds (HRAPs) are shallow, paddlewheel-mixed open raceway ponds that are an efficient and cost-effective upgrade for the conventional wastewater treatment ponds used by communities and farms the world over. HRAPs provide improved natural disinfection and nutrient removal and can be further enhanced by carbon dioxide (CO₂) addition to promote algal growth which is often carbon limited. This paper discusses the construction and operation of a 5-ha demonstration HRAP system treating primary settled wastewater at the Christchurch wastewater treatment plant, New Zealand. The system consisted of four 1.25-ha HRAPs that were constructed from an existing conventional pond. Algae were harvested from the HRAP effluent in specially designed settlers, which concentrated the algal/bacterial biomass to 1–2% organic solids for conversion to bio-crude oil following dewatering. Performance data from the first 15?months of HRAP operation (without CO₂ addition) are presented. The four demonstration HRAPs had reasonable replication of both treatment performance and algal/bacterial productivity with similar annual average wastewater treatment efficiency (~50% removal of BOD₅, ~87% removal of fBOD₅, ~65% removal of ammoniacal-N, ~19% removal of dissolved reactive phosphorus and ~2 log removal of Escherichia coli), algal species composition and algal/bacterial biomass production (~8?g?m^?2?day ?1 volatile suspended solids). These results were in good agreement with the results for pilot-scale HRAP without CO₂ addition in New Zealand. This study provides further indication of the potential for energy efficient and effective wastewater treatment using HRAP, while biofuel conversion of the harvested algal bacterial biomass could provide a valuable niche distributed energy source for local communities.     

Population dynamics of bacteria in Arctic sea ice

The dynamics of bacterial populations in annual sea ice were measured throughout the vernal bloom of ice algae near Resolute in the Canadian Arctic. The maximum concentration of bacteria was 6.0·10¹¹ cells·m^–2 (about 2.0·10¹⁰ cells·l^–1) and average cell volume was 0.473 m³ in the lower 4 cm of the ice sheet. On average, 37% of the bacteria were epiphytic and were most commonly attached (70%) to the dominant alga,Nitzschia frigida (58% of total algal numbers). Bacterial population dynamics appeared exponential, and specific growth rates were higher in the early season (0.058 day^–1), when algal biomass was increasing, than in the later season (0.0247 day^–1), when algal biomass was declining. The proportion of epiphytes and the average number of epiphytes per alga increased significantly (P<0.05) through the course of the algal bloom. The net production of bacteria was 67.1 mgC·m^–2 throughout the algal bloom period, of which 45.5 mgC·m^–2 occurred during the phase of declining algal biomass. Net algal production was 1942 mgC·m^–2. Sea ice bacteria (both arctic and antarctic) are more abundant than expected on the basis of relationships between bacterioplankton and chlorophyll concentrations in temperate waters, but ice bacteria biomass and net production are nonetheless small compared with the ice algal blooms that presumably support them.     

Phytofiltration of anaerobically digested sugarcane ethanol stillage using a macrophyte with high potential for biofuel production

Anaerobically digested stillage (ADS) requires treatment before being discharged into water bodies or soils to avoid adverse effects. Phytofiltration systems are eco-friendly technologies for wastewater treatment, and they simultaneously serve as a source of biomass for biofuel production. The aim of the present study was to investigate the phytofiltration of ADS using Azolla sp. The effects of the ADS strength (dilutions 1:?50 and 1?:?25 v/v) and initial biomass density (IBD) [15.44 (IBD1) and 23.16 (IBD2) g dry weight (dw) m^?2] on plant growth and pollutant removal were assessed. Productivities obtained at ADS 1:?50 (2.93 and 3.04 g m^?2 d^?1 for IBD1 and IBD2, respectively) were not significantly different from those of a synthetic medium (2.56 and 3.15 g m^?2 for IBD1 and IBD2, respectively). Higher organic matter removal was found using ADS at 1:?25 than that obtained using ADS 1:?50 (52.16–53.34 vs 32.29–38.16%), while no IBD effect was observed. The nutrient concentrations in ADS were reduced significantly, especially the concentrations of NH₄-N (75.11–82.54%), PO₄-P (88.72–92.90%) and SO₄-S (55.95–66.61%). The conversion of nutrients from ADS into Azolla biomass may result in an effective way to produce an attractive feedstock for biofuel production.     

Chemical oxygen demand,nitrogen and phosphorus removal by subsurface wetlands with Phragmites vegetation in different models

To improve the removal efficiency of subsurface wetlands vegetated mainly by Phragmites, pilot‐scale gravel‐based wetlands were used to treat sewage characterized by chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) pollution. For Phragmites vegetation, COD, TP and TN removal loads of wetland vegetation with Phragmites australis–Typha angustata–Scirpus validus as main species reached 0.517 g m^?2 d^?1, 0.277 g P m^?2 d^?1 and 0.023 g N m^?2 d^?1. The COD removal loads in pilot‐scale and medium‐scale (260 m² in area) wetlands with Phragmites‐monoculture vegetation were 0.62–0.64 g m^?2 d^?1, while that of P. australis–T. angustata–S. validus wetland reached 0.974 g m^?2 d^?1. Thus, the preferable poly‐culture model for Phragmites wetland vegetation was P. australis, T. angustata, S. validus and Zizania latifolia with stem density ratio of 8:1:5:1. After harvest, nitrogen and phosphorus standing stocks of wetland vegetations ranged only 2.2–9.93 g N m^?2 and 5.39–13.5 g P m^?2, respectively, as both the above ground biomass and the nitrogen and phosphorus contents of the wetland vegetation harvested in late autumn were low.     

NITROGEN AND PHOSPHORUS REMOVAL RATES WITHIN SUBUNITS OF ALGAL TURF SCRUBBERS GROWN ON DAIRY MANURE

Pizarro, C., Westhead, E. K. & Mulbry, W. Agricultural Research Service, U.S.D.A., Beltsville, MD 20705-2350 USA Conservation and reuse of nitrogen (N) and phosphorus (P) from animal manure is increasingly important as producers try to minimize transport of these nutrients off-farm. An alternative to land spreading is to grow crops of algae on the N and P present in the manure. The general goals of our research are to assess one algal production technology, termed algal turf scrubbers (ATS) to recover nutrients from animal manures. The specific objectives of these experiments were to test different loading rates of anaerobically digested dairy manure on nitrogen removal rates. Algal turfs were grown in a laboratory-scale ATS unit (1 m²) operated by recycling wastewater and adding manure effluents daily. The most abundant genera of benthic algae in the ATS unit were Ulothrix, Oedegonium and Rhizoclonium. Replicate subsamples (0.04 m²) of algal turfs of the same age were removed from the ATS unit and treated with different loads of manure containing 5–40 mg l^-1 ammonium-N (NH₄-N). During the experiments, the pH was maintained between 7–7.5 to prevent ammonia volatilization. Ammonium-N removal rates were biphasic, with a fast rate of 3.0–4.7 mg-NH₄-N hr^-1g^-1 DW for the first 20–30 minutes, followed by a slower rate of 0.53–0.96 mg-NH₄-N hr^-1g^-1 DW for the remainder of the 2 hour incubation period. The initial rates are comparable to laboratory scale ATS units and correspond to calculated removal rates of about 3 g NH₄-N m^-2d^-1.     

Annual production of leaf-decaying fungi in a woodland stream

1. Fungi are thought to be important mediators of energy flow in the detritus-based food webs of woodland streams. However, until recently, quantitative methods to assess their contribution have been lacking. Growth rates of leaf-decaying fungi can be estimated from rates of acetate incorporation into ergosterol which, together with estimates of fungal biomass from ergosterol concentrations, enables calculation of fungal production. In this study, I used this method to estimate total production of leaf-decaying fungi over an annual cycle in a small woodland stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomass and production on an areal basis, I determined the amount of leaf litter occurring in the stream by sampling transects randomly selected in each of ten 10-m sections every 20–50 days. Subsamples of leaves chosen from five of the transects were used to determine ergosterol concentrations and in situ rates of acetate incorporation into ergosterol. 2. Leaf litter, fungal biomass m^–2, and fungal production m^–2 were highly seasonal. Leaf litter ranged from 249 g m^–2 in November to less than 5 g m^–2 during the summer. Fungal biomass as percentage of leaf litter ranged from 4.4 to 8.8% during the year, but on an areal basis ranged from 11 to 13 g m^–2 during November to January to 0.25 g m^–2 in June, primarily due to the seasonal variation in amount of leaf litter present. Fungal growth rates averaged 2.6% day^–1 (0.9–7.0% day^–1) during the year. Daily production of leaf-decaying fungi ranged from 0.49 g m^–2 in November, when the amount of leaf litter was at its maximum, to 0.006 g m^–2 during the summer when the amount of leaf litter was low. Annual production of leaf-decaying fungi was 34 g m^–2, with an annual production to biomass ratio (P/B) of 8.2. 3. Fungal spore concentrations in the stream were also seasonal and were correlated with amount of leaf litter m^–2 and fungal biomass m^–2. Spore concentrations varied between one and four spores ml^–1 throughout most of the year, but increased to eighteen spores ml^–1 shortly after the greatest amount of leaf litter was present in the stream during November.     

Antarctic Stream Ecosystems: Variability in Environmental Properties and Algal Community Structure

The variability in physical, chemical and biological properties was examined for a number of glacier melt streams in south Victoria Land, Antarctica. Streams flowed for between one and two months. Stream water temperatures (range = 0–11°C) varied over short (hr) time scales whilst discharges varied considerably between streams (range 0.001–15 m³s⁻¹) and over diel cycles. Solar radiation and air temperature were major determinants of stream discharge. Variability in discharge was reflected in variability in nutrient chemistry and sediment load. Nitrogen and phosphorus varied considerably between streams; the meltwaters early in summer contained 10–20 times higher levels of dissolved N and P than later in the season. Within stream nutrient levels were modified by dense algal growths and penguin rookeries. Epilithic algal communities were made up predominantly of cyanophyceae which formed mats and crusts. Longitudinal and horizontal variability of species in the communities in selected streams is described. Analyses of algal cover and biomass (chlorophyll a) show that substrate type and flow rates are of greater importance than nutrients in influencing algal abundance and biomass. In some streams biomass values of over 20 μg Ch. a cm⁻² were recorded, much of which remains viable but inactive over the antarctic winter.     

Nitrogen and phosphorus removal rates using small algal turfs grown with dairy manure

Conservation and reuse of nitrogen (N) and phosphorus (P) from animalmanure is increasingly important as producers try to minimize transport ofthesenutrients from farms. An alternative to land spreading is to grow crops ofalgaeon the N and P present in the manure. The general goal of our research is toassess nutrient recovery from animal manure using attached algae. The specificobjective of this study was to evaluate the use of small subsections of algalturfs for determining N and P removal rates by attached algae under differentloading rates of dairy manure. Algae were grown in a laboratory–scalealgal turf scrubber (ATS) operated by recycling wastewater and adding manureeffluent daily. Replicate subsections (0.032 m²) ofalgal turf screens were removed and treated with five different loadings ofanaerobically digested dairy manure containing 5 to 80 mgL^–1 NH₄-N and 1 to 20 mgL^–1 PO₄-P over a 2-h incubationperiod. NH₄-N removal rates were biphasic with a fast initial ratefollowed by a slower rate. Biphasic rates were more pronounced for the lowestloading rates but less so for the higher ones. PO₄-P removal rateswere linear throughout the incubation period for all loading rates. N and Premoval rates increased with increasing loading rate and biomass. Inincubationsusing 1% dairy manure NH₄-N and PO₄-P removal ratesaveraged 0.72 and 0.33 g m^–2d^–1,respectively. These rates were approximately 5 to 8-fold lower than ratesmeasured on laboratory-scale ATS units using undisturbed turfs.