# Qualitative Assessment of Hazardous Gas Emissions from Sewage Sludge-Derived Biochar
## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Airflow Rate, mL\(\cdot\)min\({}^{-1}\)** & **The Reactor Headspace-to-Biochar Volume Ratio** & **Share of the Total Peak Area, \%** & **Chemical Name** & **CAS Number** & **Hazard Class and Category Code** & **Hazard Classification** \\ \hline  & & 28 & Cyclotetrasiloxane, octamethyl- & 556-67-2 & Repr. 2 Aquatic Chronic 4 & H361f (\({}^{\circ}\)) H413 \\ \cline{3-6}
250 & & 13 & Bis(2-ethylhexyl) phthalate & 117-81-7 & Repr. 1B & H360-FD \\ (1.04) & 24:1 & & 2 & Pentaonic acid & 109-52-4 & Skin Corr. 1B, Aquatic Chronic 3 & H314 H412 \\ \cline{3-6}  & & 1 & Ethylbenzene & 100-41-4 & Flam. Liq. 2 Acute Tox. 4 (\({}^{\circ}\)) & H225 H332 \\ \hline
250 & & 14 & Cyclotetrasiloxane, octamethyl- & 556-67-2 & Repr. 2 Aquatic Chronic 4 & H361f (\({}^{\circ}\)) H413 \\ (1.00) & 1:1 & & Ethylbenzene & 100-41-4 & Flam. Liq. 2 Acute Tox. 4 (\({}^{\circ}\)) & H225 H332 \\ \hline
500 & & 62 & Cyclotetrasiloxane, octamethyl- & 556-67-2 & Repr. 2 Aquatic Chronic 4 & H361f (\({}^{\circ}\)) H413 \\ (2.08) & 24:1 & & 1.4 & Styrene & 100-42-5 & Flam. Liq. 3 Acute Tox. 4 (\({}^{\circ}\)) Eye Irr. 2 Skin Irr. 2 & H226 H332 H319 \\ \hline
500 & & 19 & Cyclotetrasiloxane, octamethyl- & 556-67-2 & Repr. 2 Aquatic Chronic 5 & H361f (\({}^{\circ}\)) H413 \\ (4.00) & 1:1 & & 2.0 & Ethylbenzene & 100-41-4 & Flam. Liq. 2 Acute Tox. 4 (\({}^{\circ}\)) & H225 H332 \\ \hline  & & & 62 & Cyclotetrasiloxane, octamethyl- & 556-67-2 & Repr. 2 Aquatic Chronic 5 & H225 H332 \\ \hline  & & & 2.0 & Ethylbenzene & 100-41-4 & Flam. Liq. 2 Acute Tox. 4 (\({}^{\circ}\)) & H225 H332 \\ \hline  & & & & & & \\ \end{tabular} Notes: * Reproductive toxicity (Repr. 1A, 1B and 2), hazardous to the aquatic environment (Aquinatic Chronic 3, 4 and 5), skin corrosion/irritation (Skin Corr. 1B and Skin Irr. 2),hammable liquid (Flam. Liq. 2 and 3), acute toxicity (Acute Tox. 4), and serious eye damage/eye irritation (Fye Irrit. 2), H225 is a highly flammable liquid and vapor, H226 is a flammable liquid and vapor, H314 causes severe skin burns and eye damage, H315 causes skin irritation, H319 causes serious eye irritation, H332 is harmful if inhaled, H360-FD may damage fertility/may damage the unknown child, H361f is suspected of damaging fertility, H412 is harmful to aquatic life with long-lasting effects, and H413 may cause long-lasting harmful effects to aquatic life.  
\end{table} 
Table 2: Identified hazardous organic compounds emitted from stored biochar derived from sewage sludge. in headspace air exchange rate (from 28 to 62, Table 1). Other hazardous compounds were identified, such as bis(2-ethylhexyll) phthalate, pentanoic acid, ethylbenzene, and styrene (Table 1). Octamethyl-cyclotetrasiloxane has a hazard class 2 for reproductive toxicity and an aquatic chronic class 4, both being the highest in their respective categories. Siloxanes may be found in the biochars derived from sewage sludge, as they are present in the wastewater. Due to adsorption on the activated sludge flocks' surfaces, siloxanes are transferred from wastewater to sewage sludge [21]. Bis(2-ethylhexyll) phthalate has a reproductive toxicity hazard class of 1B. Pentanoic acid has a hazard class for skin corrosion/irritation in category 1B. Ethylbenzene is a flammable liquid with a hazard class of category 2. Styrene has a category 3 hazard class for a flammable liquid, acute toxicity with a category 4, serious eye damage/eye irritation with a category 2, and skin corrosion/irritation with a category 2. No conclusive trends could be found in the effects of the headspace-to-biochar volume ratio or air exchanges in biochar headspace. Caution should be exercised when designing biochar storage, aiming to lower the risk of occupational exposure to hazardous gas emissions. Monitoring air pollutants, tracking the highest permissible concentrations and workers' exposure, and using personal protective equipment are recommended. People working with biochar can, therefore, be exposed to the effects of hazardous organic compounds.