Integration of Microalgae Cultivation in a Biogas Production Process from Organic Municipal Solid Waste: From Laboratory to Pilot Scale

Abstract

In this study, the feasibility of integrating microalgae cultivation in a biogas production process that treats the organic fraction of municipal solid waste (OFMSW) was investigated. In particular, the biomass growth performances in the liquid fraction of the digestate, characterized by high ammonia concentrations and turbidity, were assessed together with the nutrient removal efficiency. Preliminary laboratory-scale experiments were first carried out in photobioreactors operating in a continuous mode (Continuous-flow Stirred-Tank Reactor, CSTR), to gain preliminary data aimed at aiding the subsequent scaling up to a pilot scale facility. An outdoor experimental campaign, operated from July to October 2019, was then performed in a pilot scale raceway pond (4.5 m2), located in Arzignano (VI), Italy, to assess the performances under real environmental conditions. The results show that microalgae could grow well in this complex substrate, although dilution was necessary to enhance light penetration in the culture. In outdoor conditions, nitrification by autotrophic bacteria appeared to be significant, while the photosynthetic nitrogen removal was around 12% with respect to the inlet. On the other hand, phosphorus was almost completely removed from the medium under all the conditions tested, and a biomass production between 2–7 g m−2 d−1 was obtained.

Production of Microalgal Slow-Release Fertilizer by Valorizing Liquid Agricultural Digestate: Growth Experiments with Tomatoes

“…was cultivated on diluted digestate by 1:30 [36]. Barreiro-Vescovo et al (2020) also investigated a microalgae consortium in outdoor batch and semi-continuous experiments in a 4.5 m 2 raceway pond in summer and early autumn seasons on OFMSW liquid digestate fraction diluted at 1:20 for the batch mode and 1:10 for the semi-continuous mode [41]. From day 0 to 35, the biomass concentration and productivity increased until a maximum value of 0.74 g TSS L −1 and 6.9 g TSS m 2 d −1 .…”

“…From day 0 to 35, the biomass concentration and productivity increased until a maximum value of 0.74 g TSS L −1 and 6.9 g TSS m 2 d −1 . After day 35, the concentration of TSS started to decrease until minimum values close to 0.13-0.31 g TSS L −1 corresponding to productivity values of 1.2-2.9 g TSS m 2 d −1 [41]. Finally Marin et al (2018) investigated seasonal variation of biogas upgrading coupled with digestate treatment in outdoors raceway ponds on a microalgae consortium [39].…”

Microalgae Production on Biogas Digestate in Sub-Alpine Region of Europe—Development of Simple Management Decision Support Tool

“…For example, Figler et al [80] conducted experiments cultivating microalgae in different NaCl concentrations (from 500 to 20,000 mg L −1 , corresponding to 800-36,000 µS cm −1 ) and successfully grew Scenedesmus obliquus and S. obtusus even at very high Na + concentrations. The growth inhibition of microalgae when using high EC substrates rich in ammonia-nitrogen (e.g., biogas digestate) is primarily due to the toxic effects of ammonia or other inhibitory substances rather than the salts themselves [81,82], so the dilution of these feedstocks is necessary to reduce the inhibitory effect, which also reduces EC [83].…”

Life Cycle Assessment of an Innovative Microalgae Cultivation System in the Baltic Region: Results from SMORP Project

“…A potential solution to overcome these barriers could be integrating a microalgae cultivation system with existing industrial plants. One of the most promising is CHP plants that operate with biogas produced via anaerobic digestion (AD) [36]. AD is one of the most diffused sources to produce renewable energy based on numerous bacteria' oxygen-free decomposition of organic substances.…”