Effluent quality and regulatory compliance at the GP1Z LPG/condensate complex in Arzew, Algeria: a 12-month physicochemical survey

Abstract

Industrial effluents released into the Gulf of Arzew, north-western Algeria, are subject to national limit values, yet published monitoring records for the liquefied petroleum gas and condensate complexes of that coast are scarce. This study describes one year of effluent quality at the GP1Z complex of Arzew and assesses its compliance. Treated effluents were sampled monthly during 2023 at four points: the outlets of the two parallel biological lines, the outlet of the oil-water separator, and the common discharge upstream of the marine outfall. Ten variables were determined by standard methods: temperature, pH, total suspended solids, chemical and five-day biochemical oxygen demand, total phosphorus, iron, oil and grease, total hydrocarbons and Kjeldahl nitrogen. The monitoring dataset was incomplete: 19.8% of the expected parameter-by-occasion determinations were unavailable. At the common discharge, the regulatory point of compliance, no measured value exceeded any of the ten limit values of the decree; the assessment covers 116 of the 120 expected determinations, Kjeldahl nitrogen having been measured on 8 of the 12 occasions. A pH of 6.20 recorded in January at an internal point is reported as a process observation. Against the stricter indicative values of the World Bank Group, the common discharge exceeded the phosphorus value on 11 of 12 occasions, the oil and grease value on 9 of 12 and the total-nitrogen value on 5 of 8. The common discharge was significantly the least concentrated stream for four parameters; the complete-case ordination showed similar first-axis patterns to the exploratory imputed analysis, although the explained variance differed. Recurrent phosphorus levels identify phosphorus polishing as the priority.