Todays agricultural food production highly depends on the availability of non-renewable resources like crude oil, natural gas and phosphor rocks. Tomorrow's food security can only be ensured by reducing this dependency. There are open questions concerning the methods that can be used for the production of renewable sources in order to achieve this goal.
Is it technically and economically feasible, for instance, to produce micro-algal fertilizer in photo-bio reactors to recycle N and P from waste water streams? Is this furthermore possible by avoiding the combustion of non-renewable energies to become energy self-sucient?
Relevant examples from literature will be used to investigate the microalgal potential to extract nutrients from urban waste water streams for the re-injection into the food chain of the population. The production of algae and heat will be described in a bio-physical way to calculate the mass- and
energy flux in photo-bio reactors, attached to walls of buildings in Vienna. It will be suggested to decompose the generated bio material through anaerobic digestion to increase the N- and P share on one hand and to produce methane as an energy carrier on the other hand. The calculation model will
be used to estimate the costs of producing a micro-algal fertilizer in Vienna.
Furthermore a possible utilization of the generated fertilizer in vertical farms
will be discussed.
About 271t micro algae per year could be produced on a 100m*100m wall in
Vienna. The combustion of the produced biogas could meet the entire heat and electrical-energy demand of the production process.
By demonstrating the technical feasibility of every single part of the energy self-sucient production
chain, the technical feasibility of the whole concept is ensured.
The costs of this product, however, would be nine times higher than the costs
of commercial fertilizer. The bio-re
nery in question still has a great potential when it comes to saving a high amount of non-renewable resources, thus making it an attractive alternative to the exclusive use of biomaterial as an energy carrier. This can be further shown by comparing the sunlight irradiation on a photo-bio reactor with the calori
c value of the produced micro algae: This calculation yields an energy conversion efficiency of about 4% which could be surpassed by the electricity production of every available photovoltaic system.
Table of Contents
1 Introduction
1.1 Brief history of fertilizer utilization
1.2 Resources used in today’s agriculture
1.3 Concept for the urban food supply chain of tomorrow
2 Ecological Stoichiometry
3 About the Utilization of Light
3.1 Photosynthesis by algae
3.2 Total sunlight irradiance
3.3 Reflections on the reactor surface
3.4 Absorption in algal culture
3.5 Photosynthetically active radiation
3.6 Solar conversion efficiency
3.7 Biomass yield
3.8 Calculations-Summary
4 Nutrients
4.1 Carbon dioxide
4.2 Recycling nutrients from waste water treatment plants
5 Temperature
5.1 Photosynthetically non active radiation and inhibition
5.2 Photosynthetic inefficiency
5.3 Total heat produced
5.4 Ensuring culture temperature for maximum yield
5.5 Calculations-Summary
6 Getting Energy Self-sufficient, A Harvesting Method
6.1 Raising algal density
6.2 Biogas as a joint product
6.3 Final treatment
6.4 Net energy of the harvesting process
7 Estimating Algal Fertilizer Production in Vienna
7.1 Total net energy
7.2 Costs, fertilizer value and other benefits
8 Conclusions
8.1 Sensitivity analysis
8.2 Food for thought
Objectives and Topics
This thesis investigates the technical and economic feasibility of an urban nutrient recycling system, where microalgae are cultivated in photobioreactors (PBRs) on building facades to recover nitrogen and phosphorus from wastewater, aiming to reduce dependence on non-renewable agricultural resources and improve food security.
- Closed-loop nutrient recovery (N and P) from urban wastewater.
- Bio-physical modeling of mass and energy fluxes in vertical PBR systems.
- Energy self-sufficiency via anaerobic digestion of algal biomass to produce methane (biogas).
- Economic assessment of microalgal fertilizer production compared to current market standards.
- Integration with vertical farming concepts to shorten food supply chains.
Excerpt from the Book
§ 1.3 Concept for the urban food supply chain of tomorrow
The world population prospect of the UN’s department of economic and social affairs (ESA) released different growth forecasts for the upcoming decades. Their overall conclusion is that the number of people living on this planet will increase until 2050 to a value between 8 and 12 billion [ESA, 2010]. About 9 billion people would need a 70%-increase in food supply compared to the 2005-07 period [FAO, 2009, p.2]. Looking at the previous paragraphs shows that a concept developed to meet this food demand has to consider also how to save water, land and non-renewable resources at once:
[Despommier, 2010] discusses the idea of a fully controlled agriculture. In so-called vertical farms, food could be produced minimizing cultivated area and shifting production into town at the same time. Many models have been developed in regards to the architecture and function of such farms. All of them are following the same guidelines: Multi-storeyed buildings hosting different cultivation methods should produce the nutrient demand of the citizens living within a short radius around the location of production. Different well-known techniques could ensure a year-round harvest in perfectly controlled environments. [Despommier, 2010, p.162ff] predicts that pythotrophology is advanced enough to create healthy food in an artificial environment. Some of the numerous advantages are listed below (after [Despommier, 2010, p.145ff]):
• Year-round crop production
• No weather-related crop failures
• Use of 70-95% less water
• Greatly reduced food miles
• More control over food safety and security
Summary of Chapters
Introduction: Provides the historical context of fertilizer use and explores modern challenges like resource scarcity and the necessity for sustainable, urban-based food production systems.
Ecological Stoichiometry: Establishes the fundamental chemical and elemental requirements for microalgal growth, using the Redfield ratio as a baseline for nutrient mass flow.
About the Utilization of Light: Analyzes the physics of photosynthesis, light absorption in bioreactors, and the derivation of biomass yield based on solar irradiance data.
Nutrients: Examines the sources of essential nutrients (N, P, CO2), focusing on the potential of urban wastewater streams as a viable supply for algal cultivation.
Temperature: Investigates the thermodynamic requirements for maintaining optimal growth conditions, including calculations for heating and cooling demands in an urban environment.
Getting Energy Self-sufficient, A Harvesting Method: Details the process of converting algal biomass into fertilizer and methane, focusing on energy balance and recovery techniques.
Estimating Algal Fertilizer Production in Vienna: Applies the theoretical model to a specific case study in Vienna, assessing total energy net balances and economic feasibility.
Conclusions: Summarizes the sensitivity analysis of the proposed model and discusses the broader implications for global food security and sustainable resource management.
Keywords
Microalgae, Photobioreactors, Wastewater, Nutrient Recycling, Sustainability, Urban Agriculture, Vertical Farming, Bioenergy, Biogas, Stoichiometry, Photosynthesis, Renewable Resources, Fertilizer Production, Economic Feasibility, Energy Efficiency.
Frequently Asked Questions
What is the core focus of this thesis?
The work focuses on the technical and economic potential of using urban wastewater nutrients and vertical photobioreactors to produce microalgal fertilizer, creating an energy-self-sufficient circular system for urban food supply.
Which key thematic areas are covered?
The thesis spans from biological fundamentals (stoichiometry, photosynthesis) to engineering applications (bioreactor design, energy balancing) and economic assessment (cost-benefit analysis of production).
What is the primary research question?
The research asks whether it is technically and economically feasible to produce microalgal fertilizer in urban-attached photobioreactors by recycling wastewater nutrients while maintaining energy self-sufficiency.
Which scientific methodology is applied?
The author employs a bio-physical calculation model based on literature-derived parameters to estimate biomass production, energy flux, and heat demand, supplemented by economic calculations based on local Viennese data.
What is the content of the main chapters?
The main sections cover the theory of ecological stoichiometry, the physics of light utilization in PBRs, nutrient sourcing, energy-balancing for temperature and harvesting, and a detailed economic assessment for the city of Vienna.
Which keywords define this work?
The work is characterized by terms such as microalgae, photobioreactors, nutrient recycling, vertical farming, biogas, and energy self-sufficiency.
How is the energy self-sufficiency of the process maintained?
The process aims to achieve energy self-sufficiency by utilizing methane produced from the anaerobic digestion of the harvested algal biomass to power the heating and processing steps of the production cycle.
Is the proposed fertilizer production economically competitive?
According to the calculations provided, the current concept is not yet economically feasible, with estimated production costs significantly higher than traditional mineral fertilizer prices, highlighting the need for cheaper PBR technology.
- Quote paper
- Fabian Schipfer (Author), 2012, Physics of the urban production of algae in photo-bio reactors for the utilization in vertical farms, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/205051
