A novel method to harvest <Emphasis Type="Italic">Chlorella</Emphasis> sp. by co-flocculation/air flotation

Objectives

To develop a more effective dissolved air flotation process for harvesting microalgae biomass, a co-flocculation/air flotation (CAF) system was developed that uses an ejector followed by a helix tube flocculation reactor (HTFR) as a co-flocculation device to harvest Chlorella sp. 64.01.

Results

The optimal size distribution of micro-bubbles and an air release efficiency of 96 % were obtained when the flow ratio of inlet fluid (raw water) to motive fluid (saturated water) of the ejector was 0.14. With a reaction time of 24 s in the HTFR, microalgae cells and micro-bubbles were well flocculated, and these aerated flocs caused a fast rising velocity (96 m/h) and high harvesting efficiency (94 %).

Conclusions

In a CAF process, micro-bubbles can be encapsulated into microalgae flocs, which makes aerated flocs more stable. CAF is an effective approach to harvesting microalgae.

     

Flotation of cadmium-loaded biomass

Biosorption of heavy metal ions such as Cd(2+) by dead biomass has been recognized as a potential alternative to existing removal technologies applied to wastewater treatment. Two bacterial strains were studied in the laboratory, streptomyces griseus and S. clavuligerus, an industrial by-product. Both washed and unwashed samples were examined. Foam flotation proposed in this work as the separation state following biosorption. Effective biomass separation was conducted in the presence of a frother, ethanol. The pH of the solution was a crucial parameter for flotation and also for metal binding. Other basic parameters of flotation examined were the initial cadmium concentration in the dilute aqueous solution and the quantity of biomass used. A study of zeta-potential measurements of the actinomycetes was carried out under the conditions used in the separation; surface tension was also measured. These provided useful information on the process. (c) 1994 John Wiley & Sons, Inc.     

Kinetics of nitrification in a fixed biofilm reactor using dewatered sludge-fly ash composite ceramic particle as a supporting medium

A mathematical model system was derived to describe the kinetics of ammonium nitrification in a fixed biofilm reactor using dewatered sludge-fly ash composite ceramic particle as a supporting medium. The model incorporates diffusive mass transport and Monod kinetics. The model was solved using a combination of the orthogonal collocation method and Gear’s method. A batch test was conducted to observe the nitrification of ammonium-nitrogen ( \({\text{NH}}_{4}^{ + }\) -N) and the growth of nitrifying biomass. The compositions of nitrifying bacterial community in the batch kinetic test were analyzed using PCR–DGGE method. The experimental results show that the most staining intensity abundance of bands occurred on day 2.75 with the highest biomass concentration of 46.5 mg/L. Chemostat kinetic tests were performed independently to evaluate the biokinetic parameters used in the model prediction. In the column test, the removal efficiency of \({\text{NH}}_{4}^{ + }\) -N was approximately 96 % while the concentration of suspended nitrifying biomass was approximately 16 mg VSS/L and model-predicted biofilm thickness reached up to 0.21 cm in the steady state. The profiles of denaturing gradient gel electrophoresis (DGGE) of different microbial communities demonstrated that indigenous nitrifying bacteria (Nitrospira and Nitrobacter) existed and were the dominant species in the fixed biofilm process.     

Treatment of slaughterhouse wastewater in a UASB reactor and an anaerobic filter

A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m³/day. The COD removal was 90% for OLR up to 5 kg COD/m³/day and 60% for an OLR of 6.5 kg COD/m³/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF.     

Impacts of long-term plant biomass management on soil phosphorus under temperate grassland

Aims

We assessed and quantified the cumulative impact of 20 years of biomass management on the nature and bioavailability of soil phosphorus (P) accumulated from antecedent fertiliser inputs.

Methods

Soil (0–2.5, 2.5–5, 5–10 cm) and plant samples were taken from replicate plots in a grassland field experiment maintained for 20 years under contrasting plant biomass regimen- biomass retained or removed after mowing. Analyses included dry matter production and P uptake, root biomass, total soil carbon (C), total nitrogen (N), total P, soil P fractionation, and ³¹P NMR spectroscopy.

Results

Contemporary plant production and P uptake were over 2-fold higher for the biomass retained compared with the biomass removed regimes. Soil C, total P, soluble and labile forms of inorganic and organic soil P were significantly higher under biomass retention than removal.

Conclusions

Reserves of soluble and labile inorganic P in soil were significantly depleted in response to continued long-term removal of P in plant biomass compared to retention. However, this was only sufficient to sustain plant production at half the level observed for the biomass retention after 20 years, which was partly attributed to limited mobilisation of organic P in response to P removal.

     

Influence of Extracellular Polymeric Substances on the Adsorption of Cadmium onto Three Bacterial Species

In this study, we measured the effect of EPS on Cd and proton adsorption behaviors by measuring the extent of adsorption onto biomass with and without the EPS removed via a cation exchange resin. We conducted both Cd adsorption experiments and potentiometric titrations of biomass using three common bacterial species: one Gram-positive (Bacillus subtilis) and two Gram-negative (Shewanella oneidensis, Pseudomonas putida) species. The Cd adsorption experiments were conducted as a function of metal loading in order to probe whether environmentally-low metal loadings lead to different adsorption mechanisms and roles for EPS than the higher metal loadings of most previous adsorption studies. We suspended each biomass sample in a solution of dissolved Cd in 0.01?M NaClO₄ at metal loadings of 1, 2, 5, and 74?μmol/g. Surface complexation modeling (SCM) was used to determine stability constants for the important Cd-bacteria complexes, and the effect of metal loading on the resulting calculated stability constant values was determined.

In general, the measured bulk Cd adsorption behavior is unaffected by EPS removal. However, our potentiometric titration results suggest that EPS removal does alter the distribution of site types, but not the mass-normalized total site concentration within the biomass. SCM suggests that high affinity sulfhydryl sites control Cd binding under low metal loading conditions for B. subtilis and P. putida, and that sulfhydryl sites are present both on the cells and within the EPS for these species. Conversely, the SCM results suggest that Cd-sulfhydryl binding is un-important on the EPS of S. oneidensis.     

Ethanol fermentation by flocculating yeast: Performance and stability dependence on a critical fermentation rate

Summary A system coupling fermentor and decantor permitted strong accumulation of yeast flocs that were homogeneously suspended in the reactional volume. At 100–190 g/l glucose feed practically total substrate conversion was attained. At 130 g/l glucose feed the highest productivity (18.4 g.l.h) and the highest ethanol yield (90.6%) were reached with biomass levels of 80–90 g/l. We observed that the stability of this system is limited when a critical fermentation rate (D.S_o) close to 39–40 g/l.h (with corresponding ethanol productivities of 19–20 g/l.h) is reached. Higher fermentation rates provoked de-flocculation and lost of biomass.Symbols D dilution rate (h^–1) - E ethanol (g/l) - S_r residual substrate (g/l) - S_o substrate in the feed (g/l) - X biomass (g/l) - ethanol yield (%) - DS_o fermentation rate (g/l.h) (for S_r0) - P_E ethanol productivity (g/l.h)     

Coagulant selection and sludge conditioning in a slaughterhouse wastewater treatment plant

Attempts were made in this study to examine the effectiveness of polymer addition to the aeration tank effluent prior to sludge flotation as practiced in a slaughterhouse wastewater treatment plant. The plant currently uses 10 mg/l of polymer prior to sludge flotation, but alternative, less-expensive, chemicals such as alum could be equally effective. Therefore, experiments were conducted using the Standard Jar test to determine the performance of both alum (Al2SO4.6H2O) and organic polymer. The dosages used for alum ranged between 0 and 1000 mg/l, whereas polymer dosages varied between 0 and 90 mg/l. The (optimal) removal efficiency for suspended solids in the mixed liquor was obtained at 400 mg/l for alum and 30 mg/l for polymer. It is evident that addition of alum or polymer results in significant removal of suspended solids reaching up to 99% for alum and 96% for polymer but alum produced a more compacted sludge. Removal of filterable COD was much lower in both cases since the chemicals used target the colloidal and suspended portion of the COD rather than the soluble (filterable) part of the COD.     

A kinetic model for suspended and attached growth of a defined mixed culture

Kinetic experiments were carried out in a semicontinuous wastewater treatment process called self-cycling fermentation (SCF) using a defined mixed culture and various concentrations of synthetic brewery wastewater. The same consortium, which had been previously identified as Acinetobacter sp., Enterobacter sp., and Candida sp., were used in these experiments. The overall rate of substrate removal was attributable to both suspended microbes and the biofilm that formed during the treatment process. A rate expression was developed for the SCF system for a range of synthetic wastewaters containing glucose and various initial concentrations of ethanol and maltose. The data indicated that substrate removal by the suspended cells was directly related to the biomass concentration. However, substrate removal by the biofilm was apparently not affected by the biofilm thickness and was a function of substrate concentration only.     

Removal of Cr(VI) from aqueous solutions by fruiting bodies of the jelly fungus (Auricularia polytricha)

The aim of this study was to investigate the potential to remove chromium (Cr) from aqueous solutions using the fruiting body of Auricularia polytricha. Batch experiments were conducted under various conditions, and different models were used to characterize the biosorption process. Results showed that, for both fresh and dried fruiting bodies of A. polytricha, removal efficiencies of Cr(VI) and total Cr reached maximum values at pH values of 1 and 2, respectively. The process of Cr(VI) removal by A. polytricha included the sorption process as well as the reduction of Cr(VI) to Cr(III). Spectra of X-ray photoelectron spectroscopy of the biosorbent revealed that most of the Cr loaded on the biomass surface was in the trivalent form. The Freundlich model fitted the isotherm process better than the Langmuir model in the concentration range examined. The pseudo-second-order model well described the adsorption process of Cr onto the biomass. The biosorption capacity of Cr(VI) by fruiting bodies was much higher than that by most of other biosorbents reported. The results suggest that the fruiting bodies of A. polytricha should be a promising biomaterial for Cr removal from water contaminated by the heavy metal.     

Effects of simulated feeding by snow geese on Scirpus americanus rhizomes

Summary We simulated the feeding of Greater Snow Geese (Chen caerulescens atlantica) on the rhizomes of three-square bulrush (Scirpus americanus) in a tidal marsh along the St. Lawrence River estuary in Québec. During the spring staging period, aboveground biomass is unavailable and geese feed solely on rhizomes and overwintering buds. An experiment was designed to test the effect of three factors on subsequent growth of Scirpus: the intensity of removal (3 to 77% removal of belowground biomass), the number of bites (1, 2 or 3 sections removed) and the number of adventitious buds removed (1, 2 or 3). Rhizomes were dug out in May, treated and transplanted into 85-1 basins sunk in the marsh and filled with marsh soil freed of all plant material. Growth was observed weekly until the end of the growing season in August. Shoots and rhizomes were then collected, dried and weighed to obtain biomass estimates. The net above- and belowground production of Scirpus was inversely related to the initial rhizome biomass removed. At a high level of removal (>35%), the cumulative number of shoots was significantly reduced as early as two weeks after transplantation. The relative reduction in production of the treated rhizomes compared to the control plants was also related to the intensity of removal. An increased number of bites reduced production and the removal of an increased number of adventitious buds further amplified the effect of removal on rhizome production. These experimental results show that even low intensity of feeding by Snow Geese can reduce the production of Scirpus marshes.     

Effect of stabilization on biomass activity

The study aimed to compare aerobic and aerobic/anoxic stabilization processes in terms of organic matter and the biomass removal efficiencies using a municipal sludge sample. The efficiency of stabilization process was assessed monitoring suspended solids (SS), volatile suspended solids (VSS), total and dissolved organic carbon (TOC, DOC), nitrate, nitrite, and phosphate parameters. The oxygen uptake rate (OUR) measurements were conducted to determine active biomass concentration. On the 30th day of the aerobic stabilization, the SS, VSS and TOC removal efficiencies were 22%, 28% and 55%, respectively. Under aerobic/anoxic conditions, removal efficiencies for SS, VSS and TOC were 25%, 27% and 67%. On the 17th day of the stabilization, SS and VSS removal rates were 60 mg SS/L day and 47 mg VSS/L day for aerobic and 102 mg SS/L day and 63 mg VSS/L day for aerobic/anoxic conditions, respectively. These findings reflected the higher stabilization performance of the aerobic/anoxic conditions. Based on respirometric results, the ratios of the active biomass were decreased to 30% and 24% for the 17th and 30th day of the aerobic stabilization, respectively. Such results have significant implications relative to the activity decrease quantification of the biomass as well as its further application potentials after aerobic or aerobic/anoxic sludge stabilization.     

High rate algal pond operating strategies for urban wastewater nitrogen removal

Two experimental high rate algal ponds (HRAPs) (1.5m², 570 L per unit), each with a secondaryclarifier for algal biomass separation (0.025 m²,without recirculation), were fed with urban wastewaterfor a one-year period (June 1993 to July 1994). TheHRAPs were installed on the roof of the Department ofHydraulic, Coastal and Environmental Engineering ofthe Technical University of Catalonia, Barcelona,Spain (lat. 41^° 24 42 N; long. 2^° 742 E). Nitrogen removal efficiency and changes intotal nitrogen, total organic nitrogen,NH₄ ⁺-N, and oxidized nitrogen underdifferent hydraulic retention times (HRTs) werecompared. HRAP A was always operated at a higherHRT than HRAP B. Both HRAPs were subjected to thesame environmental conditions of solar radiation, airtemperature and influent water quality. Grab samplesof influent, effluent of the HRAP (mixed liquor) andfinal effluent from the clarifiers were taken once aweek. The annual average nitrogen removal was 73% forHRAP A, and 57% for HRAP B. Higher removal in HRAP Awas due to a lower inorganic nitrogen concentration inits effluent. Significant differences (p> 0.05) inthe relative proportions of nitrogen forms between thetwo HRAPs were observed only in autumn and winter.This was mainly because HRAP B did not achieve a highlevel of NH₄ ⁺-N removal by stripping andalgal uptake, as observed in HRAP A. NH₄ ⁺-Nstripping was the most important mechanism fornitrogen removal (mean efficiency of 47% and 32% inHRAP A and B, respectively) followed by algal uptake,and subsequent algal separation in the clarifiers(mean efficiency of 26% and 25% in HRAP A and Brespectively). The conclusion of this study is thatHRT determines both the nitrogen removal efficiencyand the distribution of nitrogen forms in the effluentof a HRAP. The nitrogen removal level can becontrolled through suitable HRT operating strategies.By operating at a HRT of 4 days in spring and summer,and 10 days in autumn and winter, nitrogenconcentration in the effluent of a HRAP system can bereduced to less than 15 mg L^-1 N.     

Pathways of Increased Water Clarity After Fish Removal from Ventura Marsh; a Shallow, Eutrophic Wetland

We investigated the pathways by which water clarity increases following fish removal by evaluating the effects of a benthivorous fish reduction in a large, shallow, eutrophic, wetland in a predominately agricultural watershed in Iowa, U.S.A. Phytoplankton was phosphorus limited prior to manipulation. After a substantial fish removal was obtained, water clarity increased as a result of decreased suspended sediment and phytoplankton biomass. Trophic cascading, mitigated by release from fish predation and decreased physical interference from suspended sediments, appears to determine water clarity. Inorganic suspended solids declined immediately after fish were removed but the biomass of Daphnia and Ceriodaphnia did not increase until a few weeks after fish removal. High grazing by zooplankton likely reduced phytoplankton biomass during the height of the clear-water phase. Phytoplankton appeared to be limited by zooplankton grazing for approximately two months before reverting to bottom-up control. An increase in suspended sediment and/or increased predation pressure on zooplankton, due to the return of juvenile carp, appears to account for the decline of larger-bodied zooplankters and the switch back to bottom-up control. Macrophyte diversity and density increased substantially after the initiation of the clear-water phase.     

The importance of seed reserves for seedling performance: an integrated approach using morphological,physiological, and stable isotope techniques

To investigate how seed reserves affect early seedling performance, we conducted a factorial greenhouse experiment using Lithocarpus densiflora (Tanoak). Seedlings were grown from large (5.8±0.7 g) and small (3.2±0.4 g) seeds and, following shoot emergence, seeds were either removed or left attached. Seedlings were harvested for quantification of biomass and ¹³C at seven time periods following seed removal (2, 4, 8, 16, 32, 64, 128 days) and seedling photosynthesis was measured three separate time periods (2–4, 49–82, 95–128 days after seed removal). Biomass increased for all seedlings, but the increase was significantly larger for seedlings with attached seeds than with removed seeds. Seed removal just after shoot emergence significantly decreased seedling biomass, but seed removal 64 days after shoot emergence had no effect on seedling biomass. Seedling photosynthesis per unit leaf area varied by time and seed presence, but not by seed size. At the first period, seedlings with attached seeds had significantly higher photosynthetic rates than seedlings with removed seeds, at the second period there was no effect of seed removal, and at the third time period seedlings with attached seeds had significantly lower photosynthetic rates than seedlings with removed seeds. Despite temporal variation in photosynthesis per unit leaf area, seedlings with attached seeds always had significantly greater leaf area than seedlings with removed seeds, resulting in significantly higher total plant photosynthesis at all three time periods. The ¹³C values of both the leaves and roots were more similar to that of the seed for seedlings with attached seeds than for seedlings with removed seeds, however, seed removal and seed size strongly affected root ¹³C. This study demonstrates that seed reserves have important effects on the early growth, physiology, and ¹³C of L. densiflora seedlings.     

Parameters affecting protein production from brewery waste water in a multi-channel laboratory-scale activated sludge system

Summary With the aim of studying the possible utilization of brewery waste water activated sludge for animal feeding, the influence of the solids retention time (SRT) and nitrogen supplementation were investigated, especially with respect to biomass production and biomass composition. It was found that the SRT strongly influenced both parameters. At an SRT of from 4 to 6 days excellent biomass production was obtained. This biomass had the highest protein content and the daily protein production was four times higher than at a SRT of 20 days. Supplementation with urea doubled the protein production, lowered the carbohydrate and poly--hydroxybutyric acid content, but increased the nucleic acid content. The COD removal was better and phosphorus removal increased. In order to study these variables, a multi-channel laboratory system was designed. Because of its simplicity in operation and its versatility this system is described in detail.     

Glycerol as substrate for biomass and β-carotene production byRhodotorula lactosa

Glycerol was used as the sole carbon and energy source for growingRhodotorula lactosa. The maximum biomass yield (0.53 g/g substrate) was obtained after 20 h with 21.5 g glycerol/l; growth was inhibited with 28.0 g glycerol/l and cell morphology was changed. At this time, the cells were not pigmented. After 48 h of cultivation, -carotene was at 1.8 mg/g dry cells, yielding 22.0 mg/l. When cells were grown for 20 h, washed, suspended in distilled water and aerated for 24 hours, more -carotene (2.66 mg/g dry cells or 28.0 mg/l of the original culture) was produced. Cell protein content after 48 h was 36 to 38% (w/w) before extraction and 45 to 47% (w/w) for acetone-extracted cells.     

Nitrifying bacterial community structure of a full-scale integrated fixed-film activated sludge process as investigated by pyrosequencing

Nitrifying bacterial community structures of suspended and attached biomasses in a full-scale integrated fixed-film activated sludge process were investigated by analyzing 16S rRNA gene sequences obtained from pyrosequencing. The suspended biomass had a higher number of ammoniaoxidizing bacterial sequences (0.8% of total sequences) than the attached biomass (0.07%), although most of the sequences were within the Nitrosomonas oligotropha lineage in both biomasses. Nitrospira-like nitrite-oxidizing bacterial sequences were retrieved in the suspended biomass (0.06%), not in the attached biomass, whereas the existence of Nitrobacter-like sequences was not evident. The suspended biomass had higher nitrification activity (1.13 mg N/TSS/h) than the attached biomass (0.07 mg N/TSS/h). Overall, the results made it possible to conclude the importance of the suspended biomass, rather than the attached biomass, in nitrification in the wastewater treatment process studied.     

Continuous production of biohythane from hydrothermal liquefied cornstalk biomass via two-stage high-rate anaerobic reactors

Background

Biohythane production via two-stage fermentation is a promising direction for sustainable energy recovery from lignocellulosic biomass. However, the utilization of lignocellulosic biomass suffers from specific natural recalcitrance. Hydrothermal liquefaction (HTL) is an emerging technology for the liquefaction of biomass, but there are still several challenges for the coupling of HTL and two-stage fermentation. One particular challenge is the limited efficiency of fermentation reactors at a high solid content of the treated feedstock. Another is the conversion of potential inhibitors during fermentation. Here, we report a novel strategy for the continuous production of biohythane from cornstalk through the integration of HTL and two-stage fermentation. Cornstalk was converted to solid and liquid via HTL, and the resulting liquid could be subsequently fed into the two-stage fermentation systems. The systems consisted of two typical high-rate reactors: an upflow anaerobic sludge blanket (UASB) and a packed bed reactor (PBR). The liquid could be efficiently converted into biohythane via the UASB and PBR with a high density of microbes at a high organic loading rate.

Results

Biohydrogen production decreased from 2.34 L/L/day in UASB (1.01 L/L/day in PBR) to 0 L/L/day as the organic loading rate (OLR) of the HTL liquid products increased to 16 g/L/day. The methane production rate achieved a value of 2.53 (UASB) and 2.54 L/L/day (PBR), respectively. The energy and carbon recovery of the integrated HTL and biohythane fermentation system reached up to 79.0 and 67.7%, respectively. The fermentation inhibitors, i.e., 5-hydroxymethyl furfural (41.4–41.9% of the initial quantity detected) and furfural (74.7–85.0% of the initial quantity detected), were degraded during hydrogen fermentation. Compared with single-stage fermentation, the methane process during two-stage fermentation had a more efficient methane production rate, acetogenesis, and COD removal. The microbial distribution via Illumina MiSeq sequencing clarified that the biohydrogen process in the two-stage systems functioned not only for biohydrogen production, but also for the degradation of potential inhibitors. The higher distribution of the detoxification family Clostridiaceae, Bacillaceae, and Pseudomonadaceae was found in the biohydrogen process. In addition, a higher distribution of acetate-oxidizing bacteria (Spirochaetaceae) was observed in the biomethane process of the two-stage systems, revealing improved acetogenesis accompanied with an efficient conversion of acetate.

Conclusions

Biohythane production could be a promising process for the recovery of energy and degradation of organic compounds from hydrothermal liquefied biomass. The two-stage process not only contributed to the improved quality of the gas fuels but also strengthened the biotransformation process, which resulted from the function of detoxification during biohydrogen production and enhanced acetogenesis during biomethane production.