PROSPECTUS

Up to $50,000,000

Common Stock

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We have entered into an at-the-market sales agreement, dated August 10,  2026, or the Sales Agreement, with Robert’s & Ryan Inc, or Robert’s & Ryan, relating to shares of our common stock offered by this prospectus. In accordance with the terms of the Sales Agreement, we may offer and sell shares of our common stock, par value $0.0001 per share, having an aggregate offering price of up to $50,000,000 from time to time through Robert’s & Ryan, acting as our sales agent.

This Sales Agreement replaces our prior sales agreement, dated December 23, 2025 with Lake Street (the "Prior Sales Agreement"). No sales will be made pursuant to the Prior Sales Agreement subsequent to the date of this prospectus.  Our common stock is listed on The Nasdaq Capital Market under the symbol "SCWO." The last reported sale price of our common stock on June 11, 2026 was $2.45 per share.

As of the date of this prospectus, the aggregate market value of our outstanding common stock held by non-affiliates, or the public float, was approximately $27,000,000, which was calculated based on 11,018,601 outstanding shares of the Company’s common stock held by non-affiliates at a price of $2.45 per share, the closing price of our common stock on June 11, 2026, as reported on Nasdaq. Pursuant to General Instruction I.B.6 of Form S-3, or the "baby shelf" rules, in no event will we sell securities registered on our Form S-3 registration statement, including under our ATM, with a value of more than one-third of the aggregate market value of shares of our common stock held by non-affiliates in any 12-month period, so long as the aggregate market value of shares of our common stock held by non-affiliates is less than $75 million. After giving effect to the approximate $9,000,000 offering limit imposed by General Instruction I.B.6 of Form S-3 and deducting the shares sold within the preceding 12 months, approximately $1,142,000 shares of common stock remain available at this time for sale under our Form S-3.