Andy Shilton

Wastewater treatment high rate algal ponds for biofuel production.

While research and development of algal biofuels are currently receiving much interest and funding, they are still not commercially viable at todays fossil fuel prices. However, a niche opportunity may exist where algae are grown as a by-product of high rate algal ponds (HRAPs) operated for wastewater treatment. In addition to significantly better economics, algal biofuel production from wastewater treatment HRAPs has a much smaller environmental footprint compared to commercial algal production HRAPs which consume freshwater and fertilisers. In this paper the critical parameters that limit algal cultivation, production and harvest are reviewed and practical options that may enhance the net harvestable algal production from wastewater treatment HRAPs including CO(2) addition, species control, control of grazers and parasites and bioflocculation are discussed.

Recycling algae to improve species control and harvest efficiency from a high rate algal pond.

This paper investigates the influence of recycling gravity harvested algae on species dominance and harvest efficiency in wastewater treatment High Rate Algal Ponds (HRAP). Two identical pilot-scale HRAPs were operated over one year either with (HRAP(r)) or without (HRAP(c)) harvested algal biomass recycling. Algae were harvested from the HRAP effluent in algal settling cones (ASCs) and harvest efficiency was compared to settlability in Imhoff cones five times a week. A microscopic image analysis technique was developed to determine relative algal dominance based on biovolume and was conducted once a month. Recycling of harvested algal biomass back to the HRAP(r) maintained the dominance of a single readily settleable algal species (Pediastrum sp.) at >90% over one year (compared to the control with only 53%). Increased dominance of Pediastrum sp. greatly improved the efficiency of algal harvest (annual average of >85% harvest for the HRAP(r) compared with ∼60% for the control). Imhoff cone experiments demonstrated that algal settleability was influenced by both the dominance of Pediastrum sp. and the species composition of remaining algae. Algal biomass recycling increased the average size of Pediastrum sp. colonies by 13-30% by increasing mean cell residence time. These results indicate that recycling gravity harvested algae could be a simple and effective operational strategy to maintain the dominance of readily settleable algal species, and enhance algal harvest by gravity sedimentation.

Pond Treatment Technology

Pond treatment technology is used in tens of thousands of applications serving many millions of people across the globe - why? Simply because it is efficient and effective. While pond treatment technology offers relative simplicity in its application, it incorporates a host of complex and diverse mechanisms that work to treat and cleanse polluted waters before their return to our environment. This book offers a comprehensive review of the pond technology field including the newest ideas and latest findings. Topics covered include: This title belongs to Integrated Environmental Technology Series ISBN: 9781843390206 (Print) ISBN: 9781780402499 (eBook)

Variability and uncertainty in water demand and water footprint assessments of fresh algae cultivation based on case studies from five climatic regions

Using case studies from five typical climatic locations, this study revealed that current quantification of water demand (WD) and water footprint (WF) of freshwater algae cultivation in raceway ponds suffer from uncertainty and variability in the methodologies and assumptions used. Of particular concern, the WF metric had an intrinsically poor geographical resolution and could be biased towards high-productivity arid locations because local levels of water stress are not accounted for. Applying current methodologies could therefore cause the selection of locations that are neither economically viable nor environmentally sustainable. An improved methodology should utilize more accurate evaporation models, determine realistic limits for the maximum hydraulic retention times and process water recycling ratios, and apply weighting to the WF to reflect localized water stress or use an alternative metric such as the equivalent years of rainfall required to support a productivity of 1G J m(-2).

Mechanistic Modeling of Broth Temperature in Outdoor Photobioreactors

This study presents the first mechanistic model describing broth temperature in column photobioreactors as a function of static (location, reactor geometry) and dynamic (light irradiance, air temperature, wind velocity) parameters. Based on a heat balance on the liquid phase the model predicted temperature in a pneumatically agitated column photobioreactor (1 m(2) illuminated area, 0.19 m internal diameter, 50 L gas-free cultivation broth) operated outdoor in Singapore to an accuracy of 2.4 °C at the 95% confidence interval over the entire data set used (104 measurements from 7 different batches). Solar radiation (0 to 200 W) and air convection (-30 to 50 W)were the main contributors to broth temperature change. The model predicted broth temperature above 40 °C will be reached during summer months in the same photobioreactor operated in California, a value well over the maximum temperature tolerated by most commercial algae species. Accordingly, 18,000 and 5500 GJ year(-1) ha(-1) of heat energy must be removed to maintain broth temperature at or below 25 and 35 °C, respectively, assuming a reactor density of one reactor per square meter. Clearly, the significant issue of temperature control must be addressed when evaluating the technical feasibility, costs, and sustainability of large-scale algae production.

Universal temperature model for shallow algal ponds provides improved accuracy.

While temperature is fundamental to the design and optimal operation of shallow algal ponds, there is currently no temperature model universally applicable to these systems. This paper presents a model valid for any opaque water body of uniform temperature profile. This new universal model was tested against 1 year of experimental data collected from a wastewater treatment high rate algal pond. On the basis of 1 year of data collected every 15 min, the average errors of the predicted afternoon peak and predawn minimum were both only 1.3 °C and the average error between these extremes was just 1.2 °C. In order to demonstrate the improvement in accuracy gained, the expressions for heat fluxes used in nine prior temperature models were systematically substituted into the new universal model and evaluated against the experimental data. Errors in the peak and minimum temperatures increased by up to 2.1 and 3.2 °C, respectively, while the error between these extremes increased by up to 2.9 °C. In practical applications, these levels of inaccuracies could lead to an under/overestimation of the algal productivity and the evaporative water loss by approximately 40% and 300%, respectively.

Solar-powered aeration and disinfection, anaerobic co-digestion, biological CO2 scrubbing and biofuel production: the energy and carbon management opportunities of waste stabilisation ponds

Waste stabilisation pond (WSP) technology offers some important advantages and interesting possibilities when viewed in the light of sustainable energy and carbon management. Pond systems stand out as having significant advantages due to simple construction; low (or zero) operating energy requirements; and the potential for bio-energy generation. Conventional WSP requires little or no electrical energy for aerobic treatment as a result of algal photosynthesis. Sunlight enables WSP to disinfect wastewaters very effectively without the need for any chemicals or electricity consumption and their associated CO(2) emissions. The energy and carbon emission savings gained over electromechanical treatment systems are immense. Furthermore, because algal photosynthesis consumes CO(2), WSP can be utilised as CO(2) scrubbers. The environmental and financial benefits of pond technology broaden further when considering the low-cost, energy production opportunities of anaerobic ponds and the potential of algae as a biofuel. As we assess future best practice in wastewater treatment technology, perhaps one of the greatest needs is an improved consideration of the carbon footprint and the implications of future increases in the cost of electricity and the value of biogas.

Plant based phosphorus recovery from wastewater via algae and macrophytes.

At present, resource recovery by irrigation of wastewater to plants is usually driven by the value of the water resource rather than phosphorus recovery. Expanded irrigation for increased phosphorus recovery may be expected as the scarcity and price of phosphorus increases, but providing the necessary treatment, storage and conveyance comes at significant expense. An alternative to taking the wastewater to the plants is instead to take the plants to the wastewater. Algal ponds and macrophyte wetlands are already in widespread use for wastewater treatment and if harvested, would require less than one-tenth of the area to recover phosphorus compared to terrestrial crops/pastures. This area could be further decreased if the phosphorus content of the macrophytes and algae biomass was tripled from 1% to 3% via luxury uptake. While this and many other opportunities for plant based recovery of phosphorus exist, e.g. offshore cultivation, much of this technology development is still in its infancy. Research that enhances our understanding of how to maximise phosphorus uptake and harvest yields; and further add value to the biomass for reuse would see the recovery of phosphorus via plants become an important solution in the future.

Outdoor cultivation of temperature‐tolerant Chlorella sorokiniana in a column photobioreactor under low power‐input

Temperature‐tolerant Chlorella sorokiniana was cultivated in a 51‐L column photobioreactor with a 1.1 m2 illuminated area. The reactor was operated outdoors under tropical meteorological conditions (Singapore) without controlling temperature and the culture was mixed at a power input of 7.5 W/m3 by sparging CO2‐enriched air at 1.2 L/min (gas hold‐up of 0.02). Biomass productivity averaged 10 ± 2.2 g/

Investigating why recycling gravity harvested algae increases harvestability and productivity in high rate algal ponds.

{\rm m}_{{\rm illuminated}\,{\rm area}}^{{\rm 2}} {\rm \hbox{-} day}