Innovative, compact and energy-efficient biofilm process for nutrient removal from wastewater.

Rapid population growth, industrial development and stringent demand for treatment of wastewater require developing and emerging economies to upgrade existing wastewater treatment plants (WWTPs) or planning new WWTPs. In the context of unavailability or unaffordability of land and resources for infrastructure expansion, low cost, small footprint, less energy consumption and product reuse are some of the major factors to be considered when either upgrading or designing new WWTPs in developing and emerging economies. Although the transition from activated sludge to biofilm processes has partly solved these challenges, there are innovations that can make the processes even more compact and more efficient. Newly developed CFIC (continuous flow intermittent cleaning) process is the next generation moving bed biological wastewater treatment system and is an example for addressing these issues. The CFIC pilot studies showed promising performance for biological chemical oxygen demand and nitrogen removal as well as particle separation facilitating wastewater reuse.

Evaluation of moving bed sand filter for denitrification, suspended solids removal and very low effluent total phosphorus concentrations.

Continuously flushing moving bed sand filter was operated in pilot scale for phosphorus (P) and nitrogen removal with simultaneous particle removal. The wastewater tested was either final effluent from a municipal wastewater treatment plant (WWTP) with nitrogen removal in moving bed biofilm reactors (MBBRs) followed by coagulation and dissolved air flotation (DAF) for P and suspended solids (SS) removal, or different mixtures of this final effluent and effluent from the MBBR-stage. The study focused on the applicability to achieve low total phosphorus (TP) concentrations (below 0.1 mg/L) and suspended solids concentrations (below 10 mg SS/L), plus good denitrification (removal rate over 750 g NO3-N/m3-d), by treating wastewater having variable concentrations of TP (from 0.19 to 7.3 mg/L), SS (from 3 to 169 mg/L) and total nitrogen (from 8 to 27 mg/L). The target effluent TP limit was easily achieved when adding coagulant to WWTP effluent. With correct coagulant dose (Al/TP-molar ratio >4) and good particle removal the target effluent TP could also be reached when treating mixed WW with fairly high influent TP. Very high denitrification rates were achieved with adequate influent P concentration and external carbon source. Low denitrification rates were observed when limited by low concentrations of biodegradable carbon and phosphorus.

Novel biofilm reactor for denitrification of municipal wastewater.

A pilot-scale CFIC® (continuous flow intermittent cleaning) reactor was run in anoxic conditions to study denitrification of wastewater. The CFIC process has already proven its capabilities for biological oxygen demand removal with a small footprint, less energy consumption and low cost. The present study focused on the applicability for denitrification. Both pre-denitrification (pre-DN) and post-denitrification (post-DN) were tested. A mixture of primary treated wastewater and nitrified wastewater was used for pre-DN and nitrified wastewater with ethanol as a carbon source was used for post-DN. The pre-DN process was carbon limited and removal rates of only 0.16 to 0.74 g NOx-N/m²-d were obtained. With post-DN and an external carbon source, 0.68 to 2.2 g NO3-Neq/m²-d removal rates were obtained. The carrier bed functioned as a good filter for both the larger particles coming with influent water and the bio-solids produced in the reactor. Total suspended solids removal in the reactor varied from 20% to 78% (average 45%) during post-DN testing period and 9% to 70% (average 29%) for pre-DN. The results showed that the forward flow washing improves both the DN function and filtration ability of the reactor.

Rotating belt sieves for primary treatment, chemically enhanced primary treatment and secondary solids separation.

Fine mesh rotating belt sieves (RBS) offer a very compact solution for removal of particles from wastewater. This paper shows examples from pilot-scale testing of primary treatment, chemically enhanced primary treatment (CEPT) and secondary solids separation of biofilm solids from moving bed biofilm reactors (MBBRs). Primary treatment using a 350 microns belt showed more than 40% removal of total suspended solids (TSS) and 30% removal of chemical oxygen demand (COD) at sieve rates as high as 160 m³/m²-h. Maximum sieve rate tested was 288 m³/m²-h and maximum particle load was 80 kg TSS/m²-h. When the filter mat on the belt increased from 10 to 55 g TSS/m², the removal efficiency for TSS increased from about 35 to 60%. CEPT is a simple and effective way of increasing the removal efficiency of RBS. Adding about 1 mg/L of cationic polymer and about 2 min of flocculation time, the removal of TSS typically increased from 40-50% without polymer to 60-70% with polymer. Using coagulation and flocculation ahead of the RBS, separation of biofilm solids was successful. Removal efficiencies of 90% TSS, 83% total P and 84% total COD were achieved with a 90 microns belt at a sieve rate of 41 m³/m²-h.