Physics of the urban production of algae in photo-bio reactors for the utilization in vertical farms

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

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.