Quarterly report pursuant to Section 13 or 15(d)

Condensed Consolidated Statements of Stockholders' Equity (Deficit)

Condensed Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	May 2019 Public Offering	January 2019 Public Offering	Restricted Stock Units (RSUs)	Common Stock	Common Stock May 2019 Public Offering	Common Stock January 2019 Public Offering	Common Stock Restricted Stock Units (RSUs)	Additional Paid-in Capital	Additional Paid-in Capital May 2019 Public Offering	Additional Paid-in Capital January 2019 Public Offering	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018					38,932,437
Beginning balance at Dec. 31, 2018	$ 50,090				$ 39				$ 145,147			$ (95,096)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,998								1,998
Common stock issued during period (in shares)						11,000,000	5,175,000	357,168
Common stock issued during period		$ 20,317	$ 9,063			$ 11	$ 5			$ 20,306	$ 9,058
Common stock issued for consulting services (in shares)					1,425,271
Common stock issued for consulting services	3,044				$ 2				3,042
Net loss	(22,209)											(22,209)
Warrants related to Veolia agreement	2,312								2,312
Ending balance (in shares) at Jun. 30, 2019					56,889,876
Ending Balance at Jun. 30, 2019	64,615				$ 57				181,863			(117,305)
Beginning balance (in shares) at Mar. 31, 2019					44,727,697
Beginning balance at Mar. 31, 2019	50,278				$ 45				157,037			(106,804)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	930								930
Common stock issued during period (in shares)						11,000,000		39,350
Common stock issued during period		$ 20,317				$ 11				$ 20,306
Common stock issued for consulting services (in shares)					1,122,829
Common stock issued for consulting services	1,857				$ 1				1,856
Net loss	(10,501)											(10,501)
Warrants related to Veolia agreement	1,734								1,734
Ending balance (in shares) at Jun. 30, 2019					56,889,876
Ending Balance at Jun. 30, 2019	64,615				$ 57				181,863			(117,305)
Beginning balance (in shares) at Dec. 31, 2019					57,997,780
Beginning balance at Dec. 31, 2019	49,589				$ 58				189,422			(139,891)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,510								1,510
Common stock issued during period (in shares)								2,253,238
Common stock issued during period				$ 2				$ 2
Common stock issued for consulting services (in shares)					23,078
Common stock issued for consulting services	24								24
Net loss	(8,410)											(8,410)
Ending balance (in shares) at Jun. 30, 2020					60,274,096
Ending Balance at Jun. 30, 2020	42,715				$ 60				190,956			(148,301)
Beginning balance (in shares) at Mar. 31, 2020					59,836,897
Beginning balance at Mar. 31, 2020	46,144				$ 60				190,402			(144,318)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	554								554
Common stock issued during period (in shares)								437,199
Net loss	(3,983)											(3,983)
Ending balance (in shares) at Jun. 30, 2020					60,274,096
Ending Balance at Jun. 30, 2020	$ 42,715				$ 60				$ 190,956			$ (148,301)