William J. Oswald

Biological Transformation of Solar Energy

Publisher Summary This chapter presents a description of a hypothetical solar energy conversion plant in which an algal culture pond, algal digester, and a thermal power generator are combined to transform solar energy into electrical power. Description, specifications, and cost estimates are provided for designing, maintaining, and operating each of the units. The cost of line power as a function of latitude and photosynthetic efficiency is estimated in the chapter. According to the data and information presented, the cost of line power in the lower latitudes of the earth would be from 15 –20 mills/kw.-hr. This compares with the estimated 16.7 mills/kw.-hr. For a fission plant of equivalent capacity, but is about three times the cost of present day thermal power in the U. S. By increasing the efficiency of the solar energy collecting ponds and improvements in digester design, power costs could be decreased to the extent that solar energy would compare favorably in cost with other sources of energy in special areas of the world.

my sixty years in applied algology

I am greatly honored to present this Keynote address. My focus, even after sixty years, continues to be on the future of phycology, even though I now present mainly from the past. I am delighted to see biological and physical scientists and engineers coming together in the field of Applied Phycology. Our working together will result in many benefits for mankind. There is no doubt that Applied Phycology has a great future because it has the potential for more efficient use of solar energy than conventional agriculture, and because it is poised to reach still unimagined goals through both genetic and ecological engineering. As an engineer I have focused mainly on large algal mass culture systems and the efficient use of solar energy in wastewater treatment (Oswald, 1962, 1963). But now I can envision such future triumphs as the introduction of genes for sulfur amino acids into the presently deficient Spirulina genome. I am fascinated by Dr Bailey Green’s crusade to minimize energy use and greenhouse gas emissions using algae-based sewage treatment (Green, 1998), by Dr Joseph Weissman’s commercial production of shellfish fed mass cultured algae, and by Dr John Benemann’s vision of achieving very high productivities through physiological and genetic manipulations of the photosynthetic apparatus (Benemann, 1990), to mention just three examples currently underway by former students and colleagues. All of these and many more advances have resulted from combining biological and engineering knowledge. As a young civil engineer I was greatly surprised when I learned that the growth of one unit dry weight of algae is accompanied by release of over one and one half times as much dissolved molecular oxygen, a process powered by virtually free solar energy. How to use this low cost dissolved O2 in wastewater treatment and life support systems has consumed much of my, and many of my students’, ingenuity during the past half century. Over these years my main area of research has been the design and operation of largescale cultures of microalgae that grow commensally with bacteria in rich organic media such as domestic sewage or some industrial wastes. Not only is solar energy and the resulting ‘photosynthetic oxygenation’ nearly free, but also the nutrients in the wastewaters are free and often ideally suited for algal mass cultures. In these waste treatment ponds we only exert minimal control over the algal species that grow, but we can impose some limits through pond operations such as residence time, depth and mixing. For reasons best known to the algae themselves, we often find species of Chlorella, Scenedesmus, and Micractinium, although species of Euglena, Chlamydomonas and Oscillatoria may occur in ponds with excessive loadings or long residence times. In these wastewater-fertilized systems the role of algae is primarily for production of O2 to support bacterial growth, although nutrient uptake, adsorption of heavy metals and, indirectly, disinfection are also important functions of the algae in these systems. In the following I highlight some of the benefits of growing microalgae in wastewaters (Oswald 1978).

Energy production by microbial photosynthesis

The large amounts of microalgae produced in waste treatment ponds during sewage purification are a potential source of methane and fertiliser. If techniques can be developed for the selective cultivation of filamentous or colonial microalgae, harvesting of microalgal biomass could be accomplished by low-cost straining or sedimentation methods.

Thermochemical treatment for algal fermentation

The purpose of this study was to determine the influence of the thermochemical pretreatment process of algal fermentation on the efficiency with which algal energy is converted microbiologically to the energy in methane. The variables studies were pretreatment temperature, duration, concentration, and dosage of sodium hydroxide (NaOH). In order to optimize the thermochemical pretreatment of algae, an independent variables study was selected. The results indicate that pretreatment best efficiency was attained with a temperature of 100°C for 8 h at a concentration 3.7% solids and without NaOH. Compared with untreated algae, pretreatment improved the efficiency of methane fermentation a maximum at 33%. An orthogonal square design was selected to determine the mathematical model to describe the effects of algal thermochemical pretreatment and to determine the relative significance among the pretreatment parameters.

A controlled stream mesocosm for tertiary treatment of sewage

Freshwater stream ecosystems are well known for their capabilities for “self-purification” of sewage and other wastewaters. Unfortunately, the efficiencies of treatment are low and concentrations and volumes now discharged cannot be treated by self-purification alone. This paper describes an experiment with a stream mesocosm, in central California, USA, using controlled ecosystem methodologies in the format of an algal turf scrubber (ATSTM). This system was used to drive primary production and export in the mesocosm to bring secondary sewage to tertiary levels. The mesocosm consisted of a natural, mixed assemblage of attached periphyton, microalgae and bacteria which colonized an inclined floway 152 m long and 6.7 m wide, over which wastewater flowed in a series of pulses. The capacity of the wastewater flow varied between 436 and 889 m3 per day and various operational parameters were tested. Biomass was mechanically harvested from the floway at 1- or 2-week intervals depending upon the season. This paper presents the results for nitrogen and phosphorus removal as well as that of other contaminants and productivity of the algal turf. Nitrogen and phosphorus removal from the secondary wastewater was measured twice a week during four, 8-week quarters corresponding to the solar seasons. Nitrogen and phosphorus content of the harvested solids was also measured during these periods. Based on the percentage of nutrients in the harvested solids (3.1 % N and 2.1 % P) and the operational productivity of 35 g dry solids m−2 day−1, the yearly mean removal of nitrogen and phosphorus was 1.11 ± 0.48 gN m−2 day−1 and 0.73 ± 0.28 gP m−2 day−1, respectively. Results indicate the strong potential of controlled stream mesocosms for the removal of nutrients and other contaminants from wastewater to achieve tertiary levels.

Methane fermentation, submerged gas collection, and the fate of carbon in advanced integrated wastewater pond systems

Abstract There are several basic reasons for concern regarding the fate of carbonaceous material in waste stabilization ponds: accumulation of solids; performance and useful life of the pond system; and, the control of methane emissions. In conventional ponds methane fermentation is minimal, and carbon-rich organic matter is integrated by bacteria and microalgae which grow and settle. The integration of carbon decreases pond volume and treatment capacity and causes the ponds to age prematurely, to produce odor, and to require frequent sludge removal; and, any methane produced escapes to the atmosphere. However, if carbon-rich organics are efficiently converted to methane or to harvested microalgae, the pond system will continue to treat wastewater effectively for an extended period of time. Advanced Integrated Wastewater Pond Systems (AIWPSs) developed at the University of California fully utilize methane fermentation and microalgal cultivation to treat wastewater and to reclaim energy and nutrients. First generation AIWPSs have provided reliable municipal sewage treatment at St. Helena and Hollister, California, for 28 and 16 years, respectively, without the need for sludge removal. However, these first generation systems lack the facilities to recover and utilize the carbon-rich treatment byproducts of methane and algal biomass. The recovery of methane using a submerged gas collector was demonstrated using a second generation AIWPS prototype at the University of California, Berkeley, and the optimization of in-pond methane fermentation, the growth of microalgae in High Rate Ponds, and the harvest of microalgae by sedimentation and dissolved air flotation were studied. Preliminary data are presented to quantify the fate of carbon in the second generation AIWPS prototype and to estimate the fate of carbon in a full-scale, 200 MLD second generation AIWPS treating municipal sewage. In the experimental system, 17% of the influent organic carbon was recovered as methane, and an average of 6 g C/m 2 /d were assimilated into harvestable algal biomass. In a full-scale second generation AIWPS in a climate comparable to Richmond, California located at 37° N latitude, these values would be significantly higher — as much as 30% of the influent organic carbon would be recovered as methane and as much as 10 g C/m 2 /d would be assimilated by microalgae. These efficiencies would increase further in warmer climates with more abundant sunlight.

Unusual sources of proteins for man

Recent concern over increasing costs of food and particularly of animal products has kindled interest in cheaper sources of protein. Several food companies have put on the market meat substitutes made from spun soybean protein. More bizzare replacements for meat have also been suggested. Yeast and bacteria can be grown on petroleum products of waste materials. Algae and bacteria can be harvested from sewage treatment plants. Protein can be extruded from non‐edible leaves. These products nearly all contain large amounts of protein, vitamins and minerals, but some do not have as good biological value as animal protein. In addition many of these products contain toxic components which must be removed before they can serve as important dietary sources of protein for humans. Current information on these materials will be summarized and evaluated with a view towards recommendations to potential as animal protein substitutes.

Productivity of algae in sewage disposal

Abstract One of the highly significant and rapidly developing methods of applying solar energy to environmental problems is that of waste disposal. Many of the liquid wastes from our residences, industries and farms provide a suitable medium for micro-algae in the environment to proliferate with extreme rapidity converting solar energy to the energy in their cellular matter and to heat. The efficiency of conversion of solar energy to plant tissue often reaches 5 per cent, and the efficiency of conversion of solar energy to heat apparently reaches in excess of 90 per cent. The heat so produced is beneficial to waste disposal in several ways: for example, it accelerates both aerobic and anaerobic microbiological waste oxidation and reduction and hastens the death of pathological organisms which may be present in the waste. The release of oxygen from water during photosynthesis provides aerobic microbiological waste oxidation; and the absorption of carbon dioxide which also accompanies photosynthesis raises the p H of the waste to a point which may be lethal to any pathogenic bacteria and viruses. Depending upon the availability of solar energy and the efficiency attained, production rates for oxygen may reach 500 pounds per acre per day-a rate sufficient to continuously and fully oxidize the wastes of more than 2500 persons. Under average environmental conditions, oxygen production rates of 200 lb/day may be dependably produced.

Terrestrial approaches to integration of waste treatment

Solar energy driven physical, chemical and biological recycling of nutrients is the characteristic of the Earth-Sun system which permits life on earth to continue. Natural recycle of nutrients on Earth may literally require thousands or even millions of years to be complete, but for modern civilization to continue on Earth or in space, mankind must take charge of, and accelerate, the recycle of all essentials of life. In this paper we describe studies of two accelerated recycle systems; a solar powered energy system and an integrated feed lot. Both systems require special infrastructures permitting the accelerated physical, chemical and biological processing to occur. These systems do not integrate respiratory carbon dioxide as must be done in a complete closed ecological life support system (CELSS). The Algatron, a more complete system involving microalgal bacterial waste treatment with water, oxygen and carbon dioxide recycle was designed for use in Space Stations over 20 years ago.

Closing an Ecological System Consisting of a Mammal, Algae, and Non-Photosynthetic Microorganisms

The use of mammals and plants in a closed ecological system for possible space use is a difficult but necessary task, and this is the subject of this paper. Dr. Golueke is Associate Research Biologist and Chief Microbiologist, Sanitary Engineering Research Laboratory, University of California Engineering Field Station, Richmond. Dr. Oswald is Associate Professor of Sanitary Engineering, College of Engineering, and Associate Professor of Public Health, School of Public Health, University of California, Berkeley.