Be it further enacted, That any contract or agreement made in violation of the provisions of this Act or ordinances of the city shall be illegal and void and no expenditure shall be made thereunder, and every officer and employee who shall knowingly make or participate in any such contract or agreement or authorize or make any expenditure thereunder, and their sureties on their official bonds, and every person who shall knowingly receive such a payment, shall be jointly and severally liable to the city for the full amount so paid or received. A violation of this section by any officer or employee shall be cause for his removal.