Modifying filamentous algae nutrient scrubbers for improved wastewater treatment and harvestability - comparison with microalgae

Algae have been well studied for their abilities to treat wastewater, and several types of treatment systems have been demonstrated at a range of scales. High Rate Algae Ponds (HRAP) are a microalgae-based system and Filamentous Algae Nutrient Scrubbers (FANS) a filamentous algae-based system. For FANS, nutrient removal rates are typically lower and more variable than HRAPs, while HRAPs have lower productivity and poor harvestability. This study investigated if modifying a FANS to mimic HRAPs (using high rate algae mesocosms HRAM), with respect to hydraulic retention time (HRT) and smaller footprint, overcomes FANS limitations, while increasing wastewater treatment and resource recovery compared to HRAPs. Biomass productivity on the FANS (10.5 ± 2.9 g m-2 d-1) and FANS with CO2 addition (19.0 ± 4.8 g m-2 d-1) were significantly higher (p < 0.01) compared to the HRAMs (6.7 ± 1.4 g m-2 d-1) and HRAMs with CO2 addition (8.1 ± 1.2 g m-2 d-1). Under phosphorus replete conditions, biomass production was significantly higher on FANS (44.8 ± 14.4 g m-2 d-1) than HRAMs (5.0 ± 0.6 g m-2 d-1). Effluent quality (nutrient removal) was significantly higher (p < 0.05) for FANS compared to HRAMS, regardless of treatment. For harvesting, FANS (2.9-41%) yielded significantly higher (p < 0.01) percentage solids with, and, without dewatering/gravity harvesting compared to the HRAM (0.04-0.11%). Modifying the operation of the FANS to mimic longer HRT of HRAMs resulted in higher areal biomass productivity and nutrient removal in the FANS than the HRAM, regardless of treatment. The use of filamentous algae on FANS greatly improved the percentage solids yield in the harvested biomass without the need for energy intensive harvesting techniques. Further investigations need to be undertaken to determine if benefits will be realised at fullscale.

Dissolved organic phosphorus bioremediation from food-waste centrate using microalgae

Dissolved organic phosphorus (DOP) accounts for a substantial proportion of the total phosphorus remaining in the wastewater discharge and remains a concern for the receiving environment. This study assessed the potential of wastewater microalgae for the bioremediation of DOP from anaerobically digested food-waste centrate. For high DOP to low DIP ratio, the microalgal consortia was able to remove over 98% of DOP and 95% of total dissolved phosphorus. However, under a 1:1 ratio of DOP to DIP, the microalgal consortia was only able to remove 5% of the organic phosphorus and 76% of total dissolved phosphorus. All five main microalgal species were capable of producing alkaline phosphatase to some degree, the enzyme responsible for hydrolysing the phosphorus. For the dominant species Desmodesmus communis, total phosphatase activity reduced from 46.0 ± 2.3 mmol L^-1 h^-1 in axenic cultures to only 6.3 ± 0.7 mmol L^-1 h^-1 in presence of its microbiome. This resulted in a reduction in biomass from 209 ± 13 g m^-3 to 73 ± 5 g m^-3. For Tetradesmus dimorphus, alkaline phosphatase increased from 6.5 ± 0.3 mmol L^-1 h^-1 in the axenic culture to 169.8 ± 40.1 mmol L^-1 h^-1 in presence of both its microbiome and centrate-sourced bacteria but had little impact on biomass production. DOP removal rates across all five species, in all treatments ranged from 17 to 91%. With the exception of D. communis, the nutrient removal efficiency of DOP per unit biomass suggested luxury uptake of phosphorus into the microalgal cell. For wastewaters with low inorganic and moderate to high organic phosphorus microalgal-based wastewater treatment systems may offer a cost-effective mechanism for the removal and recovery of dissolved organic phosphorus from wastewater. Further research on refining organic phosphorus bioremediation in a range of wastewater types, particularly at pilot and full-scale, is needed.

Trade-offs between effluent quality and ammonia volatilisation with CO2 augmented microalgal treatment of anaerobically digested food-waste centrate

Diversion of food waste from landfill disposal to waste-to-energy facilities has become both an environmentally and economically viable option to support the circular bioeconomy. However, the liquid centrate produced during anaerobic digestion is high in total ammonia, with concentrations ~2000 g m^-3, and can release gaseous emissions, including ammonia, methane, CO₂ and nitrous oxide, to the atmosphere. Further treatment is required before discharge to sewer, or to the environment. Microalgal wastewater treatment systems augmented with CO₂ offer a promising and cost-effective treatment solution for reducing both total ammonia concentrations and ammonia volatilisation. In this study, we investigate the effects of augmenting CO₂ on nutrient removal and specifically nitrogen losses, as well as biomass productivity under two difference hydraulic retention times (HRT). Both CO₂ addition and HRT affect nitrogen losses, with the percentage removal of total ammonia significantly lower (p < 0.01) when CO₂ was added to the treatments, while increased HRT significantly increased (p < 0.05) total ammonia percentage removal. Total nitrogen budgets showed significantly lower (p < 0.01) abiotic nitrogen losses from the system when CO₂ was added to the culture but at the expense of effluent quality. Both total suspended solids and volatile suspended solids significantly increased (p < 0.01) under longer HRT (8 days), with CO₂ addition, while chlorophyll-a biomass significantly increased (p < 0.01) on longer HRT, regardless of CO₂ addition. These results demonstrate that, while CO₂ augmentation helped to mitigate ammonia losses to atmosphere, the trade-off was poorer effluent quality. Coupling CO₂ augmentation with longer HRT increased biomass production and nutrient removal efficiency. This study provides an insight into how simple operational changes can alleviate some of the trade-offs between atmospheric losses and effluent quality. However, in order to manage the trade-off between reduced atmospheric losses and poorer effluent quality, further optimisation of the operation of the microalgal system treating food-waste centrate is required.

Emerging Technologies in Algal Biotechnology: Toward the Establishment of a Sustainable, Algae-Based Bioeconomy

Mankind has recognized the value of land plants as renewable sources of food, medicine, and materials for millennia. Throughout human history, agricultural methods were continuously modified and improved to meet the changing needs of civilization. Today, our rapidly growing population requires further innovation to address the practical limitations and serious environmental concerns associated with current industrial and agricultural practices. Microalgae are a diverse group of unicellular photosynthetic organisms that are emerging as next-generation resources with the potential to address urgent industrial and agricultural demands. The extensive biological diversity of algae can be leveraged to produce a wealth of valuable bioproducts, either naturally or via genetic manipulation. Microalgae additionally possess a set of intrinsic advantages, such as low production costs, no requirement for arable land, and the capacity to grow rapidly in both large-scale outdoor systems and scalable, fully contained photobioreactors. Here, we review technical advancements, novel fields of application, and products in the field of algal biotechnology to illustrate how algae could present high-tech, low-cost, and environmentally friendly solutions to many current and future needs of our society. We discuss how emerging technologies such as synthetic biology, high-throughput phenomics, and the application of internet of things (IoT) automation to algal manufacturing technology can advance the understanding of algal biology and, ultimately, drive the establishment of an algal-based bioeconomy.

Microalgal bioremediation of emerging contaminants - Opportunities and challenges

Emerging contaminants (ECs) are primarily synthetic organic chemicals that have a focus of increasing attention due to either increased awareness of their potential risks to humans and aquatic biota, or only recently been detected in the aquatic environment or drinking water supplies, through improved analytical techniques. . Many ECs have no regulatory standards due to the lack of information on the effects of chronic exposure. Pharmaceuticals, personal care products, pesticides and flame retardants are some of the most frequently detected ECs in aquatic environments, with over 200 individual compounds identified, to date. Current wastewater treatment is ineffective at removing ECs and there is a vital need for the development of efficient, cost-effective EC treatment systems that can be applied to a range of scales and wastewater types. Microalgae have demonstrated potential for detoxifying organic and inorganic pollutants, with a number of large-scale wastewater treatment microalgal technologies already developed. There are three main pathways that microalgae can bioremediate ECs; bioadsorption, bio-uptake and biodegradation. Microalgal bioadsorption occurs when ECs are either adsorbed to cell wall components, or onto organic substances excreted by the cells, while bio-uptake involves the active transport of the contaminant into the cell, where it binds to intracellular proteins and other compounds. Microalgal biodegradation of ECs involves the transformation of complex compounds into simpler breakdown molecules through catalytic metabolic degradation. Biodegradation provides one of the most promising technologies for the remediation of contaminants of concern as it can transform the contaminant to less toxic compounds rather than act as a biofilter. Further research is needed to exploit microalgal species for EC bioremediation properties, such as increased bioadsorption, enhanced biodegrading enzymes and optimised growth conditions. When coupled with nutrient removal, microalgal treatment of EC can be a cost-effective viable option for the reduction of contaminant pollution in waterways.

Seasonal performance of a full-scale wastewater treatment enhanced pond system

Enhanced pond systems (EPS) consist of a series of ponds that have been designed to work in synergy to provide both cost-effective enhanced wastewater treatment and resource recovery, in the form of algal biomass, for beneficial reuse. Due to the limited number of full-scale EPS systems worldwide, our understanding of factors governing both enhanced wastewater treatment and resource recovery is limited. This paper investigates the seasonal performance of a full-scale municipal wastewater EPS with respect to nutrient removal from the liquid fraction, microalgal biomass production and subsequent removal through the system. In the high rate algal pond both microalgal productivity (determined as organic matter and chlorophyll a biomass) and NH₄-N removal varied seasonally, with significantly higher biomass and removal rates in summer than in spring (p < 0.05) or winter (p < 0.01). Microalgal biomass was not successfully harvested in the algal harvester pond (AHP), most likely due to poor flocc formation coupled with relatively short hydraulic residence time (HRT). High percentage removal rates, from sedimentation and zooplankton grazing, were achieved in the maturation pond (MP) series, particularly in winter and spring. However, in summer decreased efficiency of biomass removal and the growth of new microalgal species suggests that summer-time HRT in the MPs could be shortened. Further modifications to the operation of the AHP, seasonal changes in the HRT of the MPs and potential harvesting of zooplankton grazers are all potential strategies for improving resource recovery and producing a higher quality final discharge effluent.

Environmental drivers that influence microalgal species in fullscale wastewater treatment high rate algal ponds

In the last decade, studies have focused on identifying the most suitable microalgal species for coupled high rate algal pond (HRAP) wastewater treatment and resource recovery. However, one of the challenges facing outdoor HRAP systems is maintaining microalgal species dominance. By increasing our understanding of the environmental drivers of microalgal community composition within the HRAP environment, it may be possible to manipulate the system in such a way to favour the growth of desirable species. In this paper, we investigate the microalgal community composition in two full-scale HRAPs over a 23-month period. We compare wastewater treatment performance between dominant species and identify the environmental drivers that trigger change in community composition. A total of 33 microalgal species were identified over the 23-month period but species richness (the number of species present at any given time) was low and was not related to either productivity or nutrient removal efficiency. Species turnover of the dominant microalgae happened rapidly, typically <1 week. Changes in the influent NH₄-N concentration and zooplankton grazer numbers were significantly associated with species turnover, accounting for 80% of the changes in dominant species throughout the 23-month study period. Both nutrient removal and biomass production did not differ between the two HRAPs when the dominant species was the same or differed in the two ponds. These results suggest that microalgal functional groups are more important than individual species for full-scale HRAP performance. This study has increased our understanding of some of the environmental drivers of the microalgae within the HRAP environment, which may assist with improving wastewater treatment and resource recovery.

Winter-time CO2 addition in high rate algal mesocosms for enhanced microalgal performance

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity and CO2 augmentation is often used to overcome this limitation in summer. However, the implications of carbon limitation during winter are poorly understood. This paper investigates the effects of 0.5%, 2%, 5% and 10% CO2 addition on the winter-time performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, photosynthetic efficiency, biomass production and nutrient removal rates, along with community composition. Varying percentage CO2 addition and associated change in culture pH resulted in 3 distinct microalgal communities. Light absorption by the microalgae increased by up to 144% with CO2 addition, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. Carbon augmentation increased the maximum rate of photosynthesis by up to 172%, which led to increased microalgal biovolume by up to 181% and an increase in total organic biomass for all treatments except 10% CO2. While 10% CO2 improved light absorption and photosynthesis this did not translate to enhanced microalgal productivity. Increased microalgal productivity with CO2 addition did not result in increased dissolved nutrient (nitrogen and phosphorus) removal. This experiment demonstrated that winter-time carbon augmentation up to 5% CO2 improved microalgal light absorption and utilisation, which ultimately increased microalgal biomass and is likely to enhance total annual microalgal areal productivity in HRAPs.

Enhancing microalgal photosynthesis and productivity in wastewater treatment high rate algal ponds for biofuel production

With microalgal biofuels currently receiving much attention, there has been renewed interest in the combined use of high rate algal ponds (HRAP) for wastewater treatment and biofuel production. This combined use of HRAPs is considered to be an economically feasible option for biofuel production, however, increased microalgal productivity and nutrient removal together with reduced capital costs are needed before it can be commercially viable. Despite HRAPs being an established technology, microalgal photosynthesis and productivity is still limited in these ponds and is well below the theoretical maximum. This paper critically evaluates the parameters that limit microalgal light absorption and photosynthesis in wastewater HRAPs and examines biological, chemical and physical options for improving light absorption and utilisation, with the view of enhancing biomass production and nutrient removal.

Modifying the high rate algal pond light environment and its effects on light absorption and photosynthesis

The combined use of high rate algal ponds (HRAPs) for wastewater treatment and commercial algal production is considered to be an economically viable option. However, microalgal photosynthesis and biomass productivity is constrained in HRAPs due to light limitation. This paper investigates how the light climate in the HRAP can be modified through changes in pond depth, hydraulic retention time (HRT) and light/dark turnover rate and how this impacts light absorption and utilisation by the microalgae. Wastewater treatment HRAPs were operated at three different pond depth and HRT during autumn. Light absorption by the microalgae was most affected by HRT, significantly decreasing with increasing HRT, due to increased internal self-shading. Photosynthetic performance (as defined by Pmax, Ek and α), significantly increased with increasing pond depth and decreasing HRT. Despite this, increasing pond depth and/or HRT, resulted in decreased pond light climate and overall integrated water column net oxygen production. However, increased light/dark turnover was able to compensate for this decrease, bringing the net oxygen production in line with shallower ponds operated at shorter HRT. On overcast days, modelled daily net photosynthesis significantly increased with increased light/dark turnover, however, on clear days such increased turnover did not enhance photosynthesis. This study has showed that light absorption and photosynthetic performance of wastewater microalgae can be modified through changes to pond depth, HRT and light/dark turnover.

The effects of CO₂ addition along a pH gradient on wastewater microalgal photo-physiology, biomass production and nutrient removal

Carbon limitation in domestic wastewater high rate algal ponds is thought to constrain microalgal photo-physiology and productivity, particularly in summer. This paper investigates the effects of CO₂ addition along a pH gradient on the performance of wastewater microalgae in high rate algal mesocosms. Performance was measured in terms of light absorption, electron transport rate, photosynthetic efficiency, biomass production and nutrient removal efficiency. Light absorption by the microalgae increased by up to 128% with increasing CO₂ supply, while a reduction in the package effect meant that there was less internal self-shading thereby increasing the efficiency of light absorption. CO₂ augmentation increased the maximum rate of both electron transport and photosynthesis by up to 256%. This led to increased biomass, with the highest yield occurring at the highest dissolved inorganic carbon/lowest pH combination tested (pH 6.5), with a doubling of chlorophyll-a (Chl-a) biomass while total microalgal biovolume increased by 660% in Micractinium bornhemiense and by 260% in Pediastrum boryanum dominated cultures. Increased microalgal biomass did not off-set the reduction in ammonia volatilisation in the control and overall nutrient removal was lower with CO₂ than without. Microalgal nutrient removal efficiency decreased as pH decreased and may have been related to decreased Chl-a per cell. This experiment demonstrated that CO₂ augmentation increased microalgal biomass in two distinct communities, however, care must be taken when interpreting results from standard biomass measurements with respect to CO₂ augmentation.

Effects of two different nutrient loads on microalgal production, nutrient removal and photosynthetic efficiency in pilot-scale wastewater high rate algal ponds

When wastewater treatment high rate algal ponds (HRAP) are coupled with resource recovery processes, such as biofuel production, short hydraulic retention times (HRTs) are often favoured to increase the microalgal biomass productivity. However, short HRT can result in increased nutrient load to the HRAP which may negatively impact on the performance of the microalgae. This paper investigate the effects of high (NH4-N mean concentration 39.7 ± 17.9 g m(-3)) and moderate ((NH4-N mean concentration 19.9 ± 8.9 g m(-3)) nutrient loads and short HRT on the performance of microalgae with respect to light absorption, photosynthesis, biomass production and nutrient removal in pilot-scale (total volume 8 m(3)) wastewater treatment HRAPs. Microalgal biomass productivity was significantly higher under high nutrient loads, with a 133% and 126% increase in the chlorophyll-a and VSS areal productivities, respectively. Microalgae were more efficient at assimilating NH4-N from the wastewater under higher nutrient loads compared to moderate loads. Higher microalgal biomass with increased nutrient load resulted in increased light attenuation in the HRAP and lower light absorption efficiency by the microalgae. High nutrient loads also resulted in improved photosynthetic performance with significantly higher maximum rates of electron transport, oxygen production and quantum yield. This experiment demonstrated that microalgal productivity and nutrient removal efficiency were not inhibited by high nutrient loads, however, higher loads resulted in lower water quality in effluent discharge.

Wastewater microalgal production, nutrient removal and physiological adaptation in response to changes in mixing frequency

Laminar flows are a common problem in high rate algal ponds (HRAP) due to their long channels and gentle mixing by a single paddlewheel. Sustained laminar flows may modify the amount of light microalgal cells are exposed to, increase the boundary layer between the cell and the environment and increase settling out of cells onto the pond bottom. To date, there has been little focus on the effects of the time between mixing events (frequency of mixing) on the performance of microalgae in wastewater treatment HRAPs. This paper investigates the performance of three morphologically distinct microalgae in wastewater treatment high rate algal mesocosms operated at four different mixing frequencies (continuous, mixed every 45 min, mixed every 90 min and no mixing). Microalgal performance was measured in terms of biomass concentration, nutrient removal efficiency, light utilisation and photosynthetic performance. Microalgal biomass increased significantly with increasing mixing frequency for the two colonial species but did not differ for the single celled species. All three species were more efficient at NH4-N uptake as the frequency of mixing increased. Increased frequency of mixing supported larger colonies with improved harvest-ability by gravity but at the expense of efficient light absorption and maximum rate of photosynthesis. However, maximum quantum yield was highest in the continuously mixed cultures due to higher efficiency of photosynthesis under light limited conditions. Based on these results, higher microalgal productivity, improved wastewater treatment and better gravity based harvest-ability can be achieved with the inclusion of more mixing points and reduced laminar flows in full-scale HRAP.

Increased pond depth improves algal productivity and nutrient removal in wastewater treatment high rate algal ponds

Depth has been widely recognised as a crucial operational feature of a high rate algal pond (HRAP) as it modifies the amount of light and frequency at which microalgal cells are exposed to optimal light. To date, there has been little focus on the optimisation of microalgal performance in wastewater treatment HRAPs with respect to depth, with advice ranging from as shallow as possible to 100 cm deep. This paper investigates the seasonal performance of microalgae in wastewater treatment HRAPs operated at three different depths (200, 300 and 400 mm). Microalgal performance was measured in terms of biomass production and areal productivity, nutrient removal efficiency and photosynthetic performance. The overall areal productivity significantly increased with increasing depth. Areal productivity ranged from 134 to 200% higher in the 400 mm deep HRAP compared to the 200 mm deep HRAP. Microalgae in the 400 mm deep HRAP were more efficient at NH4-N uptake and were photosynthetically more efficient compared to microalgae in the 200 mm deep HRAP. A higher chlorophyll-a concentration in the 200 mm deep HRAP resulted in a decrease in photosynthetic performance, due to insufficient carbon supply, over the course of the day in summer (as indicated by lower α, Pmax and oxygen production) compared to the 300 and 400 mm deep HRAPs. Based on these results, improved areal productivity and more wastewater can be treated per land area in the 400 mm deep HRAPs compared to 200 mm deep HRAPs without compromising wastewater treatment quality, while lowering capital and operational costs.

Annual growth layers as proxies of past growth conditions for benthic microbial mats in a perennially ice-covered Antarctic lake

Perennial microbial mats can be the dominant autotrophic community in Antarctic lakes. Their seasonal growth results in clearly discernible annual growth layering. We examined features of live microbial mats from a range of depths in Lake Hoare, Antarctica, that are likely to be preserved in these layers to determine their potential as proxies of past growth performance. Cyanobacteria dominated the mat for all but the deepest depth sampled. Changes in areal concentrations of phycobilin pigments, organic matter and extracellular polysaccharide and in species composition did not correspond to changes in various water column properties, but showed a linear relationship with irradiance. Carbonate accumulation in the mats correlated with biomass markers and may be inferred as an index of mat performance. We examined the carbonate content of annual layers laid down from 1958-1959 to 1994-1995 in sediment cores from 12 m depth. The carbonate content in the layer showed a significant correlation with the mean summer air temperature. These data suggest a link between air temperature and microbial mat growth performance, and suggest that it is mediated via irradiance. Laminated microbial mats in Antarctic lakes have the potential to act as fine-resolution records of environmental conditions in the recent past, although interpretation is complex.

Physiological determinants of climbing-specific finger endurance and sport rock climbing performance

The aim of the study was to examine several physiological responses to a climbing-specific task to identify determinants of endurance in sport rock climbing. Finger strength and endurance of intermediate rock climbers (n = 11) and non-climbers (n = 9) were compared using climbing-specific apparatus. After maximum voluntary contraction (MVC) trials, two isometric endurance tests were performed at 40% (s = 2.5%) MVC until volitional exhaustion (continuous contractions and intermittent contractions of 10 s, with 3 s rest between contractions). Changes in muscle blood oxygenation and muscle blood volume were recorded in the flexor digitorum superficialis using near infra-red spectroscopy. Statistical significance was set at P < 0.05. Climbers had a higher mean MVC (climbers: 485 N, s = 65; non-climbers 375 N, s = 91) (P = 0.009). The group mean endurance test times were similar. The force-time integral, used as a measure of climbing-specific endurance, was greater for climbers in the intermittent test (climbers: 51,769 N x s, s = 12,229; non-climbers: 35,325 N x s, s = 9724) but not in the continuous test (climbers: 21,043 N x s, s = 4474; non-climbers: 15,816 N x s, s = 6263). Recovery of forearm oxygenation during rest phases (intermittent test) explained 41.1% of the variability in the force-time integral. Change in total haemoglobin was significantly greater in non-climbers (continuous test) than climbers (P = 0.023--40% test timepoint, P = 0.014--60% test timepoint). Pressor responses were similar between groups and not related to the force-time integral for either test. We conclude that muscle re-oxygenation during rest phases is a predictor of endurance performance.

The influence of cimetidine versus ranitidine on doxepin pharmacokinetics

The effect of cimetidine and ranitidine on doxepin pharmacokinetics was studied in 6 healthy volunteers. Each subject completed 3 study phases: Treatment A, 9 consecutive doses of 50 mg doxepin (once daily); Treatment B, same as Treatment A but co-administration of cimetidine 600 mg b.i.d. starting after the sixth doxepin dose and continuing until approximately 2 days following discontinuation of doxepin administration; Treatment C, identical to Treatment B but with ranitidine 150 mg b.i.d. instead of cimetidine. Unlike ranitidine, cimetidine co-administration resulted in a significant increase in steady state plasma levels of doxepin (4.7, 9.0 and 4.5 ng/ml during Treatments A, B and C respectively) but not desmethyldoxepin (4.1, 4.6 and 4.2 ng/ml during Treatments A, B and C respectively). Elimination half-lives of doxepin and desmethyldoxepin were prolonged by cimetidine co-administration (19.6 and 26.2 h respectively), but remained unchanged during the ranitidine treatment phase (13.3 and 18.4 h) as compared to the control phase i.e. Treatment A (13.2 and 19.0 h). These results show that cimetidine, unlike ranitidine, significantly inhibits the biotransformation of doxepin. This data has clinical implications when the co-administration of tricylic antidepressants and H2-receptor antagonists are indicated.