Pulp and Paper Mill in Santiago, Chile

Project Background

Pulp and paper mill wastewater contains large amounts of lignin, resin acids, chlorinated organic compounds, and other recalcitrant substances, with high COD, BOD, and color. This mill produces approximately 300,000 tons of pulp annually, discharging about 40,000 m³/day of wastewater. The original treatment system was a conventional activated sludge process, but performance was unstable. Nitrification was particularly poor during winter when water temperatures dropped to around 10°C, leading to frequent ammonia nitrogen exceedances.

MBBR Retrofit Solution

MBBR Media was integrated into the existing activated sludge tank, converting the system into an IFAS (Integrated Fixed‑Film Activated Sludge) configuration—essentially a hybrid of activated sludge and MBBR. The filling ratio was 35%, and the original sludge return system was retained. This approach is especially effective for maintaining nitrification capacity under low‑temperature conditions.

Retrofit Results

● Ammonia nitrogen removal efficiency increased from 55% in winter to an annual average of 92%.

● COD removal efficiency improved from 85% to 94%.

● Treatment capacity increased by 30% without adding tank volume.

● Biomass increased by about 40%, greatly improving system stability.

● Sludge settleability improved, with SVI reduced by 30%.