( ( Four ( of ( ( the ( ( most important ) classes ) ) ( of ( pollutants ( in ( domestic wastewaters ) ) ) ) ) ) ) ( ( are ( ( ( ( ( nitrogen compounds ) , ) ( ( ( ( ( biochemical ( oxygen demand ) ) ( -LRB- ( BOD -RRB- ) ) ) , ) phosphorus ) , ) ) and ) ( ( total ( suspended solids ) ) ( -LRB- ( TSS -RRB- ) ) ) ) ) . ) )
(ROOT (S (NP (NP (CD Four)) (PP (IN of) (NP (NP (DT the) (ADJP (RBS most) (JJ important)) (NNS classes)) (PP (IN of) (NP (NP (NNS pollutants)) (PP (IN in) (NP (JJ domestic) (NNS wastewaters)))))))) (VP (VBP are) (NP (NP (NN nitrogen) (NNS compounds)) (, ,) (NP (NP (NP (JJ biochemical) (NN oxygen) (NN demand)) (PRN (-LRB- -LRB-) (NP (NNP BOD)) (-RRB- -RRB-))) (, ,) (NP (NN phosphorus)) (, ,)) (CC and) (NP (NP (JJ total) (VBN suspended) (NNS solids)) (PRN (-LRB- -LRB-) (NP (NNP TSS)) (-RRB- -RRB-))))) (. .)))
Four of the most important classes of pollutants in domestic wastewaters are nitrogen compounds, biochemical oxygen demand (BOD), phosphorus, and total suspended solids (TSS).
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD four) (NNS classes)) (PP (IN of) (NP (JJ biochemical) (NNS compounds))))) (. .)))