Transfer printing of vertical-type microscale light-emitting diode array onto flexible substrate using biomimetic stamp.

We report the transfer printing of GaN-based microscale vertical-type light-emitting diodes (µ-VLEDs) using a functional layer and a biomimetic stamp. An oxide-based functional layer is inserted onto the structure of a µ-VLED and used to separate the chip from the µ-VLED wafer by absorbing the pulse of a UV pulse laser during pick-up of the transfer printing process. Polydimethylsiloxane (PDMS)-based biomimetic stamps have been fabricated to mimic the gecko lizard cilia for improved adhesion and repeatability. The biomimetic stamp has an adhesion force of 25.6 N/cm2, which is 12 times the adhesion of a flat stamp; an adhesion force of 10 N/cm2 or more was maintained after 100,000 repeated adhesion tests. A flexible 10 × 10 prototype array on a polyimide substrate was fabricated, and its bending test results indicated that the strain effect on the forward voltage and the output power was less than 1%. The stable bending test results of the prototype indicate that µ-VLEDs using biomimetic stamps allow the necessary stability for practical transfer printing.

The effects of biodegradable poly(lactic-co-glycolic acid)-based microspheres loaded with quercetin on stemness, viability and osteogenic differentiation potential of stem cell spheroids.

OBJECTIVE: Quercetin has been reported to exert many beneficial effects on the protection against various diseases, such as diabetes, cancer, and inflammation. The aim of this study is to evaluate the potential osteogenic differentiation ability of mesenchymal stem cells in the presence of quercetin. MATERIAL AND METHODS: Quercetin-loaded poly(lactic-co-glycolic acid) microspheres were prepared using an electrospraying technique. Characterization of the microspheres was evaluated with a scanning electron microscope and release profile. Three-dimensional cell spheroids were fabricated using silicon elastomer-based concave microwells. Qualitative results of cellular viability were seen under a confocal microscope, and quantitative cellular viability was evaluated using the Cell Counting Kit-8 assay. The alkaline phosphatase activity and Alizarin Red S staining were performed. A quantitative real-time polymerase chain reaction and a western blot analysis were performed. RESULTS: Spheroids were well formed irrespective of quercetin concentration. Most of the cells in spheroids emitted green fluorescence, and the morphology was round without significant changes. The application of quercetin-loaded microspheres produced a significant increase in the alkaline phosphatase activity. The real-time polymerase chain reaction results showed a significant increase in Runx2, and western blot results showed higher expression of Runx2 protein expression. CONCLUSION: Biodegradable microspheres loaded with quercetin produced prolonged release profiles with increased mineralization. Microspheres loaded with quercetin can be used for the enhancement of osteoblastic differentiation in cell therapy.

Differences in the oral health status and oral hygiene practices according to the extent of post-stroke sequelae.

Oral health and hygiene are crucial parameters in stroke patients. However, few studies have evaluated the oral health status and oral hygiene practices according to the level of function in stroke patients. The aim of this study was to evaluate the oral health status and oral hygiene practices according to ambulation and personal hygiene levels in patients with stroke. Data from the fifth (2010-2012) and sixth (2013-2015) editions of the Korea National Health and Nutrition Examination Survey (KNHANES) for 6 years were combined. A total of 700 stroke patients were enrolled in our study. Subjective oral health was significantly poorer in patients who experienced a moderate problem with walking (adjusted OR [AOR], 1.68; 95% CI, 1.21-2.33) and bed-bound patients (AOR, 2.92; 95% CI, 1.01-8.44) than in patients who could walk without difficulty. Patients who were unable to bathe or dress independently exhibited a significantly higher risk of dental caries than did those who could perform the same activities unassisted. The probability of brushing teeth ≥2 times daily was 69% lower in bed-bound patients (AOR, 0.31; 95% CI, 0.11-0.87) than in patients who could walk without difficulty and 76% lower in patients who were unable to bathe or dress independently (AOR, 0.24; 95% CI, 0.09-0.62) than in those who could perform the same activities without difficulty. There were differences in oral health status and oral hygiene practices, according to ambulation level and functional independence, in the stroke patient group. These results indicate the need for oral care for stroke patients who exhibit ambulatory and functional limitations.

Anakinra Protects Against Serum Deprivation-Induced Inflammation and Functional Derangement in Islets Isolated From Nonhuman Primates.

We investigated whether serum deprivation induces islet amyloid polypeptide (IAPP) oligomer accumulation and/or a proinflammatory response and, if so, whether the addition of interleukin (IL)-1 receptor antagonist to the culture medium can relieve the proinflammatory response during serum-deprived culture of nonhuman primate (NHP) islets. After culture in medium with and without Ana under serum-deprived culture conditions, IAPP oligomer/amyloid accumulation, in vitro viability, islet function, cytokine secretion, and posttransplantation outcome in streptozotocin-induced diabetic nude mice were determined in islets isolated from heterozygote human IAPP transgenic (hIAPP+/- ) mice and/or NHP islets. Serum deprivation induced accumulation of IAPP oligomer, but not amyloid, in NHP islets. Anakinra (Ana) protected islets from the serum deprivation-induced impairment of in vitro viability and glucose-stimulated insulin secretion and attenuated serum deprivation-induced caspase-1 activation, transcription, and secretion of IL-1ß, IL-6, and tumor necrosis factor-α in hIAPP+/- mice and NHP islets. Supplementation of medium with Ana during serum-deprived culture also improved posttransplantation in vivo outcomes of NHP islets. In conclusion, serum deprivation induced accumulation of IAPP oligomers and proinflammatory responses in cultured isolated islets. Supplementation of the culture medium with Ana attenuated the functional impairment and proinflammatory responses induced by serum deprivation in ex vivo culture of NHP islets.

Obesity is inversely related to the risks of dental caries in Korean adults.

OBJECTIVE: This study investigated whether obesity is linked with dental caries. This study hypothesized that obesity may influence the number or prevalence of dental caries in Korean adults. SUBJECTS AND METHODS: Data were derived from Korea National Health and Nutrition Examination Survey performed at 2008-2010. Lifestyle, sociodemographic, and biochemical variables were analyzed. Indices related to obesity, sarcopenia, and metabolic syndrome were investigated. Finally, caries index and oral health behaviors were included for the analysis. RESULTS: The caries index was inversely associated with increasing body mass index (BMI) and body fat quartile (all p-values <.01). Subjects with high waist circumference who met the inclusion criteria of metabolic syndrome were less likely to have decayed tooth (p-value = .0009). Subjects with a BMI of 25 or more showed about 20% less prevalence of dental caries experience than normal individuals with a BMI of 18.5 to 23 glucose (odds ratio [95% confidence intervals] = 0.808 [0.684-0.956]). Similarly, subjects with total body fat in the highest quartile revealed about 20% less prevalence of caries experiences that those with body fat proportion in the lowest quartile (0.84 [0.672,1.049]). CONCLUSIONS: Obesity was inversely associated with occurrence or severity of dental caries in Korean adults.

Type 2 diabetes as a risk indicator for dental caries in Korean adults: the 2011-2012 Korea national health and nutrition examination survey.

OBJECTIVES: The associations between type 2 diabetes (T2D) and untreated dental caries was examined. This study hypothesized that there would be a positive association between T2D and the prevalence of decayed permanent teeth (DT) in representative Korean adults. METHODS: The information was derived from the Korea National Health and Nutrition Examination Survey conducted in 2011-2012. Sociodemographic and lifestyle variables, anthropometric and biochemical status, metabolic health and glucose tolerance status, oral health behaviors, and dental caries index were evaluated. RESULTS: The number of DT had a positive association with degree of fasting plasma glucose (FPG) level, and glycated hemoglobin (HbA1c) (p-value = 0.045 and 0.007, respectively). The levels of FPG and HbA1c increased with the number of DT (p for trend = 0.009 and 0.004, respectively). The prevalence of untreated caries uncontrolled T2D participants was about 26% higher than those with normal glucose tolerance levels after adjusting for potential confounders including diets and socioeconomic status (OR [95% CI] = 1.26 [1.02, 1.56]). CONCLUSIONS: T2D is an independent risk indicator for untreated caries in Korean adults.

The Introduction of Human Heme Oxygenase-1 and Soluble Tumor Necrosis Factor-α Receptor Type I With Human IgG1 Fc in Porcine Islets Prolongs Islet Xenograft Survival in Humanized Mice.

Apoptosis during engraftment and inflammation induce poor islet xenograft survival. We aimed to determine whether overexpression of human heme oxygenase-1 (HO-1) or soluble tumor necrosis factor-α receptor type I with human IgG1 Fc (sTNF-αR-Fc) in porcine islets could improve islet xenograft survival. Adult porcine islets were transduced with adenovirus containing human HO-1, sTNF-αR-Fc, sTNF-αR-Fc/HO-1 or green fluorescent protein (control). Humanized mice were generated by injecting human cord blood-derived CD34(+) stem cells into NOD-scid-IL-2Rγ(null) mice. Both HO-1 and sTNF-αR-Fc reduced islet apoptosis under in vitro hypoxia or cytokine stimuli and suppressed RANTES induction without compromising insulin secretion. Introduction of either gene into islets prolonged islet xenograft survival in pig-to-humanized mice transplantation. The sTNF-αR-Fc/HO-1 group showed the best glucose tolerance. Target genes were successfully expressed in islet xenografts. Perigraft infiltration of macrophages and T cells was suppressed with decreased expression of RANTES, tumor necrosis factor-α and IL-6 in treatment groups; however, frequency of pig-specific interferon-γ-producing T cells was not decreased, and humoral response was not significant in any group. Early apoptosis of islet cells was suppressed in the treatment groups. In conclusion, overexpression of HO-1 or sTNF-αR-Fc in porcine islets improved islet xenograft survival by suppressing both apoptosis and inflammation. HO-1 or sTNF-αR-Fc transgenic pigs have potential for islet xenotransplantation.

Novel echocardiographic indicator for potential cardioembolic stroke.

BACKGROUND AND PURPOSE: In many cardioembolic strokes (CSs), the specific embolic source is uncertain. Despite the high mortality of CS, not enough attention is paid to its potential source. Although atrial fibrillation (AF) is the most common source of embolism, more complex and dynamic multiplicities may influence CS. The aim of this study was to evaluate novel indicators of transthoracic echocardiography (TTE) that have additional value for detecting CS. METHODS: In total, 1878 patients with acute ischaemic stroke who had TTE during admission were identified. Of the patients with undetermined etiology, 93 patients with incomplete evaluations were excluded. Thereafter, two stroke neurologists reviewed all of the magnetic resonance images to assess cardioembolic lesion patterns. The patients were classified into two groups: potential cardioembolic stroke (PCS) and non-PCS. RESULTS: Amongst a total of 1601 patients, 518 (32.4%) had PCS. About half of the patients with PCS had AF. Patients with PCS were more likely to have larger left ventricular (LV) end-diastolic diameters, larger LV end-systolic diameters, larger left atrial sizes, increased E/A ratios and reduced LV ejection fractions. After adjusting for multiple clinical and TTE variables including AF, an E/A ratio ≥1.5 had a significant predictive value for PCS (odds ratio 2.89, 95% confidence interval 1.57-5.31, P < 0.01). CONCLUSION: An E/A ratio ≥1.5 is independently associated with PCS after adjusting for multiple covariates including AF and provides incremental prognostic information for detecting PCS.

Isolation and characterization of human mesenchymal stem cells from gingival connective tissue.

BACKGROUND AND OBJECTIVE: The main purpose of this study was to isolate and characterize gingival connective tissue-derived mesenchymal stem cells (GMSCs). The secondary purpose was to present a modified isolation method for the GMSCs. MATERIAL AND METHODS: Collected healthy gingival tissue samples were de-epithelialized and minced into small fragments. The tissues were digested by dispase and collagenase IV for 30 min. The first digested cell suspension was discarded, and then additional digestion was performed to the remaining cells in the same solution for 90 min. The isolated cells from gingiva was incubated in 37°C humidified condition and observed by inverted microscope. Cytoskeletal morphology was evaluated by phalloidin immunofluorescence. Potency of the cells was tested by colony-forming unit fibroblast assay. GMSCs were characterized by osteogenic, adipogenic and chondrogenic differentiation, and flow cytometric, immunofluorescence analysis. RESULTS: GMSCs showed spindle-shaped, fibroblast-like morphology, colony-forming abilities, adherence to plastic and multilineage differentiation (osteogenic, adipogenic, chondrogenic) potency. GMSCs expressed CD44, CD73, CD90 and CD105, but did not express CD14, CD45, CD34 and CD19 in flow cytometry. Expression of stem cell markers (SSEA-4, STRO-1, CD146, CD166 and CD271) and a mesenchymal marker (vimentin) were observed by immunofluorescence. CONCLUSIONS: In conclusion, we isolated and characterized stem cells from human gingival connective tissue with modified protocol. GMSCs showed multipotency with high proliferation and characteristics of mesenchymal stem cells. GMSCs are promising sources for tissue engineering and may be obtained during routine procedures under local anesthesia. Further research is needed to evaluate the potential of GSMCs' proliferation and cryopreservation.

Effect of algal recycling rate on the performance of Pediastrum boryanum dominated wastewater treatment high rate algal pond.

Recycling a portion of gravity harvested algae promoted the dominance of a rapidly settling colonial alga, Pediastrum boryanum (P. boryanum) and improved both biomass productivity and settleability in High Rate Algal Pond (HRAP) treating domestic wastewater. The effect of algal recycling rate on HRAP performance was investigated using 12 replicate mesocosms (18 L) that were operated semi-continuously under ambient conditions. Three experiments were conducted during different seasons with each experiment lasting up to 36 days. Recycling 10%, 25%, and 50% of the 'mass' of daily algal production all increased total biomass concentration in the mesocosms. However, recycling >10% reduced the organic content (volatile suspended solids (VSS)) of the mesocosm biomass from 83% to 68% and did not further increase biomass productivity (based on VSS). This indicates that if a HRAP is operated with a low algal concentration and does not utilise all the available sunlight, algal recycling increases the algal concentration up to an optimum level, resulting in higher algal biomass productivity. Recycling 10% of the daily algal production not only increased biomass productivity by ∼40%, but increased biomass settleability by ∼25%, which was probably a consequence of the ∼30% increase in P. boryanum dominance in the mesocosms compared with controls without recycling.

Increased incidence of herpes zoster in the setting of cytomegalovirus preemptive therapy after kidney transplantation.

BACKGROUND: Herpes zoster (HZ) is a common infectious disease after kidney transplantation (KT). The incidence of HZ may increase during cytomegalovirus (CMV) preemptive therapy. We therefore evaluated the incidence, risk factors, and clinical outcomes of HZ after KT, according to the type of CMV prophylaxis used. METHODS: We retrospectively established a cohort of KT recipients who underwent transplantation from June 2008 to May 2010. Patients were categorized into 3 groups according to CMV prophylaxis regimen: Group A (preemptive therapy), Group B (universal prophylaxis <3 months), and Group C (universal prophylaxis >3 months). The incidence rate of HZ was compared in each group, and risk factors for HZ were identified. RESULTS: The incidence rate of HZ was 46.6 (95% confidence interval [CI] 31.4-66.5) per 1000 person-years. The incidence rate was higher in Group A than in Group C (80.0 vs. 13.0 per 1000 person-years; P = 0.001). Median onset time of HZ after KT was shorter in Group A than in Group B (0.9 vs. 9.9 months; P < 0.001) and Group C (0.9 vs. 14.8 months; P = 0.008). Post-herpetic neuralgia occurred in 7 patients (23%). No visceral involvement or death was related to HZ. By multivariate analysis, only female gender (corrected relative risk 1.59; 95% CI 1.09-2.00) was independently associated with HZ development. CONCLUSIONS: In the setting of CMV preemptive therapy, a differentiated varicella zoster virus-specific prophylaxis might be necessary for patients with HZ risk factors.

Optimally enhanced optical emission in laser-induced breakdown spectroscopy by combining spatial confinement and dual-pulse irradiation.

In laser-induced breakdown spectroscopy (LIBS), a pair of aluminum-plate walls were used to spatially confine the plasmas produced in air by a first laser pulse (KrF excimer laser) from chromium (Cr) targets with a second laser pulse (Nd:YAG laser at 532 nm, 360 mJ/pulse) introduced parallel to the sample surface to re-excite the plasmas. Optical emission enhancement was achieved by combing the spatial confinement and dual-pulse LIBS (DP-LIBS), and then optimized by adjusting the distance between the two walls and the interpulse delay time between both laser pulses. A significant enhancement factor of 168.6 for the emission intensity of the Cr lines was obtained at an excimer laser fluence of 5.6 J/cm(2) using the combined spatial confinement and DP-LIBS, as compared with an enhancement factor of 106.1 was obtained with DP-LIBS only. The enhancement mechanisms based on shock wave theory and reheating in DP-LIBS are discussed.

Prevalence of low LDL-cholesterol levels and elevated high-sensitivity C-reactive protein levels in apparently healthy Korean adults.

BACKGROUND AND AIMS: The Justification for the Use of Statins in Primary Prevention: An Intervention Trial Evaluating Rosuvastatin (JUPITER) reported reduced cardiovascular and all-cause mortality in patients with elevated C-reactive protein (CRP) and low LDL-cholesterol (LDL-C) levels treated with statins. The aims of this study were to determine the proportion of "JUPITER-eligible" Korean adults and to describe their characteristics. METHODS AND RESULTS: As many as 15,154 subjects with serum LDL-C levels <130 mg/dL were selected among 28,851 middle-aged participants (men ≥ 50 years, women ≥ 60 years) who participated in a routine health check-up program. Among the participants with LDL-C less than 130 mg/dL, only 15% had CRP levels ≥2.0 mg/L (7.9% of original participants). Subjects were divided into four groups according to CRP levels (<0.5, ≥0.5 - <1.0, ≥1.0 - <2.0, and ≥2.0 mg/L). Mean HDL-C and apolipoprotein A1 levels decreased significantly as the mean CRP values increased. The insulin and homeostasis model of insulin resistance was significantly different according to CRP quartile. The number of subjects with metabolic syndrome and its components increased significantly as the mean CRP values increased. CONCLUSION: In this Asian population, few individuals with low LDL-C levels had CRP levels ≥2.0 mg/L. Elevated CRP levels were associated with components of atherogenic dyslipidemia and insulin resistance. Additional clinical trials should be designed and performed in different ethnic groups, as different CRP cut-off levels may be required in different ethnic groups.

A prospective longitudinal study evaluating the usefulness of a T-cell-based assay for latent tuberculosis infection in kidney transplant recipients.

We evaluated whether ELISPOT assay can predict tuberculosis (TB) development in kidney-transplantation (KT) recipients with a negative tuberculin skin test (TST). All adult patients admitted to a KT institute between June 2008 and December 2009 were enrolled; TB development after KT was observed between June 2008 and December 2010. Isoniazid (INH) was given to those patients with positive TST or clinical risk factors for latent TB infection (LTBI). ELISPOT assay was performed on all patients, and TB development after KT was observed by a researcher blinded to the results of ELISPOT. A total of 312 KT recipients including 242 (78%) living-donor KT were enrolled. Of the 312 patients, 40 (13%) had positive TST or clinical risk factors for LTBI and received INH; none developed TB after KT. Of the remaining 272 patients, 4 (6%) of 71 with positive ELISPOT assay developed TB after KT, whereas none of the 201 patients with negative (n = 171) or indeterminate ELISPOTs (n = 30) developed TB after KT (rate difference between positive and negative/indeterminate ELISPOT, 3.3 per 100 person-years [95% CI 1.4-5.1, p<0.001]). Positive ELISPOT results predict subsequent development of TB in KT recipients in whom LTBI cannot be detected by TST or who lack clinical risk factors for LTBI.

Resonant excitation of precursor molecules in improving the particle crystallinity, growth rate and optical limiting performance of carbon nano-onions.

A catalyst-free and highly efficient synthetic method for growing carbon nano-onions (CNOs) in open air has been developed through the laser resonant excitation of a precursor molecule, ethylene, in a combustion process. Highly concentric CNO particles with improved crystallinity were obtained at a laser wavelength of 10.532 µm through the resonant excitation of the CH(2) wagging mode of the ethylene molecules. A higher growth rate up to 2.1 g h( - 1) was obtained, compared with that without a laser (1.3 g h( - 1)). Formation of the CNOs with ordered graphitic shells is ascribed to the decomposition of polycyclic aromatic hydrocarbons (PAHs) into C(2) species. The optical limiting performances of the CNOs grown by the combustion processes were investigated. CNOs grown at 10.532 µm laser excitation demonstrated improved optical limiting properties due to the improved crystallinity.

An elevated apolipoprotein B/AI ratio is independently associated with microalbuminuria in male subjects with impaired fasting glucose.

BACKGROUND AND AIMS: The ratio of apolipoprotein B/AI (apo B/AI) has been used as a marker to predict the risk of coronary artery disease. Recent studies have suggested an association between apolipoprotein B level and microalbuminuria in diabetic subjects. This study was performed to assess a possible association between the apo B/AI ratio and microalbuminuria in male subjects with impaired fasting glucose (IFG). METHODS AND RESULTS: In 1266 patients with fasting serum glucose level in the pre-diabetic range, urine albumin-to-creatinine ratio (UACR, µg mg(-1)) was measured from single morning voided urine. The presence of microalbuminuria was defined as a UACR between 30 and 299 µg mg(-1). Participants were stratified into four groups by apo B/AI quartiles, from the lowest to the highest. Apo B/AI was higher with increasing body mass index, higher serum triglyceride and serum low-density lipoprotein cholesterol, systolic and diastolic blood pressure values, but lower with higher high-density lipoprotein cholesterol concentrations. After adjusting for these and other confounding factors, an increased apo B/AI ratio was independently associated with the presence of microalbuminuria. In receiver operating characteristic (ROC) curve analyses, apo B/AI ratio showed the highest correlation with the presence of microalbuminuria among the variables, although statistically not different. CONCLUSION: These findings indicate that apo B/AI ratio shows significant association with microalbuminuria in Korean male subjects with IFG.

Nutrient removal in wastewater treatment high rate algal ponds with carbon dioxide addition.

The influence of CO2 addition to high rate algal ponds (HRAPS) on nitrogen removal was investigated using two pilot-scale HRAPs operated with different hydraulic retention times (HRT: 4 and 8 days), and was compared to the nitrogen removal by the 8-day HRT pond before CO2 addition was installed. Nitrogen balances were calculated by partitioning total nitrogen into organic and inorganic nitrogen (NH4+-N and NO3--N), and by separation of the organic nitrogen into particulate (PON) and dissolved organic nitrogen (DON). PON was further divided into algal organic nitrogen (AON) and bacteria organic nitrogen (BON) to investigate nitrogen mass flow in the HRAPS. This research shows that the proportion of algae in the algal/bacterial biomass in the longer 8-day HRT HRAP8d (55.6%) was appreciably lower than that in the shorter 4-day HRT HRAP4d (80.5%) when CO2 was added to control the maximum pH to <8.0 during the summer. Higher bacterial biomass in the longer 8-day HRT HRAP corresponded with higher nitrification rates, indicating that the longer 8-day HRT in the summer was detrimental for two reasons: lower algal productivity and increased nitrogen loss through nitrification/denitrification. Overall nitrogen removal of approximately 60% in the HRAPS with CO2 addition was mainly achieved by algal assimilation followed by sedimentation in the settling unit.

Algal production in wastewater treatment high rate algal ponds for potential biofuel use.

Wastewater treatment High Rate Algal Ponds with CO2 addition could provide cost-effective and efficient tertiary-level wastewater treatment with the co-benefit of algal biomass production for biofuel use. Wastewater grown algal biomass can have a lipid content of 10-30% of dry weight, which could be used to make biodiesel. This research investigated algal biomass and total lipid production by two pilot-scale wastewater treatment HRAP(S) (4-day HRT) with and without CO2 addition under New Zealand mid summer (Nov-Jan) conditions. The influence of CO2 addition on wastewater treatment performance was also determined. CO2 was added to one of the HRAPs (the HRAP(E)) by maintaining the maximum pH of the pond below 8. Measurements of HRAP influent and effluent water qualities, total lipid content and algal biomass production were made twice a week over the experimental period. Both HRAP(S) achieved high levels of organic compound and nutrient removal, with >85% SBOD5, >92 NH4(+)-N and >70% DRP removal. Algal/bacterial biomass production in the HRAP(E) (15.2 g/m2/d) was improved by CO2 addition by approximately 30% compared with that of the control HRAP(W) (10.6 g/m2/d). Total lipid content of the biomass grown on both HRAP(S) was slightly reduced (from 25% to 20%) with CO2 addition and the maximum total lipid content of approximately 40% was observed in the HRAP(W) when low NH4(+)-N concentration (<0.5 mg/L) and high maximum pH (>10.0) occurred. Total lipid content of the biomass increased by approximately 15% under nitrogen limiting conditions, however, overall algal/bacterial biomass production was reduced by half during the period of nitrogen limitation. More research is required to maintain algal production under near nitrogen-limiting conditions.

Wastewater treatment and algal production in high rate algal ponds with carbon dioxide addition.

High rate algal ponds (HRAPs) provide improved wastewater treatment over conventional wastewater stabilisation ponds; however, algal production and recovery of wastewater nutrients as algal biomass is limited by the low carbon:nitrogen ratio of wastewater. This paper investigates the influence of CO(2) addition (to augment daytime carbon availability) on wastewater treatment performance and algal production of two pilot-scale HRAPs operated with different hydraulic retention times (4 and 8 days) over a New Zealand Summer (November-March, 07/08). Weekly measurements were made of influent and effluent flow rate and water qualities, algal and bacterial biomass production, and the percentage of algae biomass harvested in gravity settling units. This research shows that the wastewater treatment HRAPs with CO(2) addition achieved a mean algal productivity of 16.7 g/m(2)/d for the HRAP(4d) (4 d HRT, maximum algae productivity of 24.7 g/m(2)/d measured in January 08) and 9.0 g/m(2)/d for the HRAP(8d) (8 d HRT)). Algae biomass produced in the HRAPs was efficiently harvested by simple gravity settling units (mean harvested algal productivity: 11.5 g/m(2)/d for the HRAP(4d) and 7.5 g/m(2)/d for the HRAP(8d) respectively). Higher bacterial composition and the larger size of algal/bacterial flocs of the HRAP(8d) biomass increased harvestability (83%) compared to that of HRAP(4d) biomass (69%).