Developing applications for biochar in a circular economy : a review of addition to biodegradable polymers

Increasing the application fields for biochar presents an opportunity to replace fossil-fuel derived products with carbon-neutral biomass. However, to do so successfully the biomass, process requirements, product-use and end-of-life must be appropriately researched and evaluated. In this review biochar applications beyond soil were conceptually mapped and the addition of biochar to produce composites was identified as a niche theme with biodegradable plastics in particular showing promising potential for further development in the context of a circular economy. A meta-analysis of 20 bio-composite characterisation studies found that biochar up to 20 wt % produced from various feed-stocks and under differing pyrolysis conditions can lead to viable, or even biocomposites with improved properties for a number of bio-polymers. A set of recommendations for future biochar-PLA composite characterisations was suggested based on a qualitative evaluation of the publications under review. Due to the foundational nature of the research further biochar characterisation, biodegradation studies and sequential applications for biocomposites were identified as key future topics to evaluate if biochar-biocomposites are a promising application in a low-carbon circular economy

Identifying substrates for greywater treatment in a novel green wall system based on trickling filters

Green walls with greywater treatment capabilities can play a key role to close water cycles in growing cities worldwide. Most green wall systems for greywater treatment apply a similar process as in constructed wetlands, where the substrate acts as plant substrate and to treat the polluted water. A novel green wall system is in development that separates the plant layer from the greywater treatment, by introducing a setup similar to a trickling filter. In a first step, various commercial substrates were tested for their suitability in terms of treatment performance at two different hydraulic loading rates over a 10-week period, using synthetic greywater. Measured parameters for determining pollutant removal were turbidity, chemical oxygen demand (COD), and others over a treatment time of seven days, measuring concentrations at the beginning, after three days and at seven days. The first substrate, expanded shale, performed best, achieving removal rates up to 60% for COD, closely followed by the other two substrates, plastic Hel-x and foam carriers. Generally, most pollutants were removed within the first three days of treatment. Even though plastic Hel-x carriers were not as efficient in pollutant removal as expanded clay, the carrier will be used for planned pilot trials of the novel green wall system due to their lower weight

Local Water Loop : Vorstudie für einen energie- und wasserautarken Waschmaschinenbetrieb

Während der Bedarf an Süsswasser weltweit stetig steigt, wird dessen Verfügbarkeit immer knapper. Um dem entgegenzuwirken, ist die lokale Behandlung und Wiederverwendung von Grauwasser ein vielversprechender Ansatz. Von besonderem Interesse sind der Einsatz von grünen Wänden, als platzsparende Alternative zu Pflanzenkläranlagen, und Filtersäulen zur biologischen Reinigung des Abwassers. Im vorliegenden Projekt wurden die Grundlagen für einen energie- und wasserautarken Waschmaschinenbetrieb, basierend auf der biologischen Reinigungstechnologie, erarbeitet. Es wurde eine Reihe von Experimenten durchgeführt, um Waschmaschinenabwasser zu charakterisieren, eine geeignete Vorreinigung auszuwählen, ein geeignetes Filtersubstrat für die grüne Wand zu identifizieren, die Keimbelastung zu analysieren und den Energieautarkiegrad zu bestimmen und zu optimieren. Die Analyse des Waschmaschinenabwassers zeigte, dass ein Grossteil der Verschmutzung im Abwasser vom Waschmittel selbst stammt. Daher ist die Verwendung eines ökologischen Waschmittels und dessen korrekte Dosierung essenziell für einen ressourceneffizienten Betrieb. Für die physikalisch-mechanische Vorreinigung wurden ein Sandfilter und ein Feinfilter getestet. Aufgrund der hohen Faserbelastung im Waschmaschinenabwasser zeigte sich der Sandfilter als ungeeignet, da er schnell verstopfte. Stattdessen konnte mit dem Feinfilter eine gute Vorreinigung erzielt werden. Die Faserbelastung im Waschmaschinenabwasser betrug durchschnittlich 25 mg/L vor der Vorreinigung und konnte durch den Feinfilter auf 2 mg/L reduziert werden. Die Analyse der Reinigungsleistung verschiedener Substrate für die grüne Wand, darunter Vulkaponic, Vulkaponic/Pflanzenkohle-Mischung und Perlit, zeigte, dass mit reinem Vulkaponic die besten Ergebnisse erzielt wurden. Die Reinigungseffizienz von Vulkaponic betrug im Durchschnitt 85%, während die Mischung aus Vulkaponic und Pflanzenkohle eine Reinigungsleistung von 78% aufwies. Perlit erreichte eine Reinigungsleistung von 62%. Die Keimbelastung im Kreislaufsystem der Waschmaschine nimmt nach der Reinigung und UV-Behandlung stetig ab, sodass die Wasserqualität den Anforderungen an Badegewässer entspricht. Die Konzentration der aeroben mesophilen Keime sank von 130’000 KBE/mL auf 1’400 KBE/mL nach der UV-Behandlung. Dies bestätigt die Effektivität der angewandten Reinigungs- und Desinfektionsverfahren. Um den Energieautarkiegrad über ein Jahr zu bestimmen, wurden die gemessenen Werte auf ein Jahr extrapoliert. In der jetzigen Ausführung kann somit ein Autarkiegrad von 30% erzielt werden. Durch den Einsatz zusätzlicher Optimierungsmassnahmen wie die Nutzung von zusätzlichen Solarpanels und einer optimierten Steuerung kann dieser Wert auf 66% erhöht werden. Am Zielstandort in Kapstadt, Südafrika könnte damit ein Autarkiegrad von 86% erreicht werden. Die gewonnenen Erkenntnisse aus den Experimenten dienen dazu, den energie- und wasserautarken Waschmaschinenbetrieb in Folgeprojekten weiterzuentwickeln und zu optimieren

Quality and suitability of fecal biochar in structurally stable urban tree substrates

This study examines the effects of pyrolyzed materials (biochar) from horse manure, plant residues and human feces on the growth of 1-year old birch seedlings cultivated in a novel, structurally stable tree substrate. For this purpose, the composition of the produced biochar, the leachate from the substrates and the health and growth rate of the birch seedlings were observed over a period of 322 days. The results show that each of these biochars complies with the European Biochar Certificate (EBC) guidelines. No toxic heavy metals were detected. Furthermore, the presence of the biochar in the substrates enhanced the survival rate of the birch trees

Bioponics—An Organic Closed-Loop Soilless Cultivation System: Yields and Characteristics Compared to Hydroponics and Soil Cultivation

Sustainable food production has become increasingly important. Soilless cultivation systems offer several advantages, such as water and nutrient use efficiency, and can be implemented where traditional agriculture is impossible. Bioponic systems use locally or regionally available nutrient sources from organic waste streams (either fluid or solid) and can thus contribute to closing nutrient cycles locally. Bioponics harnesses the metabolic processes of microorganisms which release nutrients from organic matter. This study aimed to set up a bioponic system, by using biogas digestate concentrate and biochar as nutrient sources, and promoting nutrient release from the organic sources by including a biofilter in the system. The development of water quality, plant growth, and quality was monitored extensively. In addition, the influence of either the fungal biocontrol agent Trichoderma atrobrunneum or UV-C treatment of the nutrient solution on plant health and growth was investigated. Three cultivation cycles with Lactuca sativa (“HAWKING” Salanova®) in bioponic (BP), hydroponic (HP), and soil (SO) cultivation were performed. The study showed that healthy lettuces could be produced in BP systems, using a biogas digestate concentrate and biochar as nutrient sources, despite salt accumulation in the nutrient solution. In plant sap analyses, lettuces cultivated in BP systems contained less nitrate but more ammonium and chloride. The yield of the lettuces grown in the BP systems was intermediate, compared to the HP and the SO. The fungus, T. atrobrunneum, strain, T720, survived in soil and soilless cultivation systems. Compared to the HP and the SO systems, the shoot height of lettuces grown in the BP system, with the application of Trichoderma, was significantly increased. In SO systems with Trichoderma application, a significantly higher chlorophyll and flavonoid content, but significantly lower shoot height was observed. The fresh weight of lettuce roots was significantly higher in HP systems with Trichoderma treatment. Cultivating plants by using organic waste streams requires commitment and experience from producers. In BP systems, a biofilter (either within the system or externally, to increase nutrient levels) can help to rapidly convert the ammonium-rich fertilizer to plant-available nutrients. Unlike conventional HP systems, in BP systems, nutrients are released slowly over time, requiring close monitoring and adjustments. In conclusion, healthy lettuces for human consumption can be produced in BP systems, and the application of the biocontrol agent used has some beneficial influence on plant growth

Estimation of countrywide N2O emissions from wastewater treatment in Switzerland using long-term monitoring data

Nitrous oxides (N2O) emissions contribute to climate change and stratospheric ozone depletion. Wastewater treatment is an important, yet likely underestimated, source of N2O emissions, as recent, long-term monitoring campaigns have demonstrated. However, the available data are insufficient to representatively estimate countrywide emission due to the brevity of most monitoring campaigns. This study showed that the emission estimates can be significantly improved using an advanced approach based on multiple continuous, long-term monitoring campaigns. In monitoring studies on 14 full-scale wastewater treatment plants (WWTPs), we found a strong variability in the yearly emission factors (EFs) (0.1 to 8% of the incoming nitrogen load) which exhibited a good correlation with effluent nitrite. But countrywide data on nitrite effluent concentrations is very limited and unavailable for emission estimation in many countries. Hence, we propose a countrywide emission factor calculated from the weighted EFs of three WWTP categories (carbon removal, EF: 0.1–8%, nitrification only: 1.8%, and full nitrogen removal: 0.9%). However, EF of carbon removal WWTPs are still highly uncertain given the expected variability in performance. The newly developed approach allows representative, country-specific estimations of the N2O emissions from WWTP. Applied to Switzerland, the estimations result in an average EF of 0.9 to 3.6% and total emissions of 410 to 1690 tN2O-N/year, which corresponds to 0.3–1.4% of the total greenhouse gas emissions in Switzerland. Our results demonstrate that better data availability and an improved understanding of long-term monitoring campaigns is crucial to improve current emission estimations. Finally, our results confirm several measures to mitigate N2O emissions from wastewater treatment; year-round denitrification, limiting nitrite accumulation, and stringent control of sludge age in carbon removal plants