J.M. Garrido

Anaerobic filter reactor performance for the treatment of complex dairy wastewater at industrial scale

The wastewaters discharged by raw milk quality control laboratories are more complex than the ones commonly generated by dairy factories because of the presence of certain chemicals such as sodium azide or chloramphenicol, which are used for preserving milk before analysis. The treatment of these effluents has been carried out in a full-scale plant comprising a 12 m(3) anaerobic filter (AF) reactor and a 28 m(3) sequential batch reactor (SBR). After more than 2 years of operation, a successful anaerobic treatment of these effluents was achieved, without fat removal prior to the anaerobic reactor. The organic loading rates maintained in the AF reactor were 5-6 kg COD/m(3) d, with COD removal being higher than 90%. No biomass washout was observed, and most of the fat contained in the wastewaters was successfully degraded. The addition of alkalinity is crucial for the maintenance of a proper buffer medium to ensure pH stability. The effluent of the AF reactor was successfully treated in the SBR reactor, and a final effluent with a COD content below 200 mg/l and total nitrogen below 10mg N/l was obtained.

Effect of two broad-spectrum antibiotics on activity and stability of continuous nitrifying system.

The effects of two broad-spectrum antibiotics, chloramphenicol and oxytetracycline hydrochloride, on the microbial activity and biofilm stability of a mixed nitrifying culture were studied. These antibiotics are present in some wastewaters generated in cattle farms or pharmaceutical industries. A 1-L fermentor, in which nitrifiers grew both in suspension and in a biofilm, was used during the experiments. Chloramphenicol (10–250 mg/L) barely had any effect on biofilm stability and nitrification. Ammonia was fully oxidized to nitrate. However, oxytetracycline caused biofilm sloughing at concentrations of 10 mg/L, but nitrification was not inhibited at antibiotic concentrations up to 100 mg/L. When the concentration of oxytetracycline chlorohydrate was increased stepwise from 100 to 250 mg/L, nitrification was inhibited by 50%. The dissolved organic carbon measurements in both the influent and effluent showed that the antibiotics were neither mineralized by the mixed nitrifying culture nor accumulated in the system. Furthermore, the microbial tests did not reveal the presence of active antibiotics in the effluent. This fact indicates that both cloramphenicol and oxytetracycline were degraded by the nitrifying sludge but not mineralized.

Struvite crystallization versus amorphous magnesium and calcium phosphate precipitation during the treatment of a saline industrial wastewater.

Struvite crystallization (MgNH(4)PO(4)·6H(2)O, MAP) could be an alternative for the sustainable and economical recovery of phosphorus from concentrated wastewater streams. Struvite precipitation is recommended for those wastewaters which have high orthophosphate concentration. However the presence of a cheap magnesium source is required in order to make the process feasible. For those wastewater treatment plants (WWTP) located near the seashore magnesium could be economically obtained using seawater. However seawater contains calcium ions that could interfere in the process, by promoting the precipitation of amorphous magnesium and calcium phosphates. Precipitates composition was affected by the NH(4)(+)/PO(4)(3-) molar ratio used. Struvite or magnesium and calcium phosphates were obtained when NH(4)(+)/PO(4)(3-) was fixed at 4.7 or 1.0, respectively. This study demonstrates that by manipulating the NH(4)(+)/PO(4)(3-) it is possible to obtain pure struvite crystals, instead of precipitates of amorphous magnesium and calcium phosphates. This was easily performed by using either raw or secondary treated wastewater with different ammonium concentrations.

Simultaneous urea hydrolysis, formaldehyde removal and denitrification in a multifed upflow filter under anoxic and anaerobic conditions.

A multifed upflow filter (MUF), working under anoxic or anaerobic conditions, coupled with an aerobic biofilm airlift suspension (BAS) reactor was operated in order to treat a wastewater with high formaldehyde (up to 1.5 g L-1) and urea (up to 0.46 g L-1) concentrations. In the MUF, formaldehyde removal, denitrification and urea hydrolysis took place simultaneously. The MUF was operated at 37 degrees C, at a hydraulic retention time (HRT) ranging from 1 to 0.3 d. An organic loading rate (OLR) of 0.5 kg-formaldehyde m-3 d-1 was efficiently eliminated during anaerobic operation and transformed into methane, while a much higher OLR (up to 2 kg-formaldehyde m-3 d-1) was oxidised under anoxic conditions by the nitrite or nitrate from the nitrifying airlift. However, only 80% of urea was hydrolysed to ammonia in an anoxic environment while complete conversion occurred under anaerobic conditions. Moreover, formaldehyde concentrations higher than 50 mg L-1 provoked a loss of efficiency of urea hydrolysis, decreasing to 10% at formaldehyde concentrations above 300 mg L-1. Methane production rate during the anaerobic stage was adversely affected by accumulations of formaldehyde in the reactor causing lower formaldehyde removal efficiency. However, denitrification proceeded properly even at a formaldehyde concentration of 700 mg L-1 in the reactor, although nitrous oxide appears in the off-gas. The COD/N ratios required for complete nitrite and nitrate denitrification with formaldehyde were estimated at 2.1 and 3.5 kg-COD/kg-N, respectively.

Impact of methanogenic pre-treatment on the performance of an aerobic MBR system

The combination of anaerobic treatment with an aerobic MBR as a polishing step is an alternative to treat some industrial wastewater and/or urban wastewaters generated in warm climate countries. In this work a pilot-scale UASB reactor and an aerobic MBR as a polishing step was operated. The impact of the methanogenic stage on membrane fouling was studied. Operating fluxes of 11-18 L m(-2) h(-1) and permeabilities of 100-250 L m(-2) h(-1) bar(-1) were reported. It was demonstrated that the recirculation of aerobic biomass to the anaerobic stage provoked a release of biopolymers due to the hydrolysis of aerobic biomass in these conditions. Depending on biomass concentration in membrane chamber, the presence of biopolymers worsened membrane performance. Fouling rate was three times higher when biomass concentration decreased from 8 to 2 g L(-1), with similar concentrations of biopolymers present. Moreover, the presence of plastic support in the aerobic stage was shown to improve membrane performance, decreasing the concentrations of the studied fouling indicators. Carbohydrate fraction of soluble microbial products, biopolymer clusters (BPC) and transparent exopolymer particles (TEP) concentrations were studied as possible fouling indicators for this system. A strong correlation between both colloidal fraction of BPC (cBPC) and TEP with membrane fouling rate was observed.

The effect of kaolin particles on the behavior of nitrifying activated sludge units.

The effects of the addition of powered particles of kaolin to nitrifying activated sludge systems were studied. Kaolin was added to a nitrifying activated sludge reactor, during the operational phase, to observe the effects of this clay on reactor performance. The results were compared to those obtained from a similar unit operated without kaolin. The settling properties of the sludges from both units were similar (sludge volume index (SVI) of 14.5 ml/g VSS; zone settling velocity (ZSV) of 7.5 m/h), but the specific nitrifying activities of ammonia and nitrite oxidizing processes were enhanced up to 75% and 50%, respectively, when kaolin was added. The mechanism of action of kaolin was not clear. Additional ammonia, nitrite and nitrate adsorption tests showed that these compounds were not adsorbed by kaolin. This demonstrated that no beneficial effect was caused by adsorption of either substrates or products. Short-term activity tests also showed that the stimulating effects of kaolin on specific activity were not immediate. The effects of kaolin when nitrifying units were operated under unfavorable conditions were also evaluated: In a second set of experiments, a nitrifying unit was operated with low levels of dissolved oxygen (DO), with and without kaolin. The presence of kaolin exerted practically no effect on ammonia oxidation but nitrite oxidation slightly diminished. In a third set of experiments, a nitrifying unit was subjected to pH shocks (9, 10 and 11) over 3 h with pH then restored to 7.8. A pH shock of 11 caused a decrease of 60% in nitrifying activity for 12 days. When kaolin was added to this unit the efficiency of the system was completely restored in 4 days. Therefore, kaolin might be useful to restore damaged units.

Advanced Monitoring and Supervision of Biological Treatment of Complex Dairy Effluents in a Full-Scale Plant

The operation of a wastewater treatment plant treating effluents from a dairy laboratory was monitored by an advanced system. This plant comprises a 12 m3 anaerobic filter (AF) reactor and a 28 m3 sequential batch reactor (SBR) coupled in series and is equipped with the following on‐line measurement devices: biogas flow meter, feed and recycling flow meters, temperature sensor, dissolved oxygen analyzer, and redox meter. Other parameters such as chemical oxygen demand (COD), volatile fatty acids (VFA), etc. were determined off‐line. The plant has been in operation for 634 days, the influent flow rate being 6–8 m3/d. COD concentration of the influent ranged between 8 and 12 kg COD/m3, resulting in COD values in the effluent around 50–200 mg/L. The behavior of the system was studied using the set of measurements collected by the data acquisition program especially developed for this purpose. Monitoring of variables such as anaerobic reactor temperature permitted the detection and prevention of several failures such as temperature shocks in the AF reactor. Besides, off‐line measurements such as the alkalinity or the VFA content, together with the on‐line measurements, provided immediate information about the state of the plant and the detection of several anomalies, such as organic overloads in the SBR, allowing the implementation of several fast control actions.

Enhancement of struvite pellets crystallization in a full-scale plant using an industrial grade magnesium product

A full-scale struvite crystallization system was operated for the treatment of the centrate obtained from the sludge anaerobic digester in a municipal wastewater treatment plant. Additionally, the feasibility of an industrial grade Mg(OH)2 as a cheap magnesium and alkali source was also investigated. The struvite crystallization plant was operated for two different periods: period I, in which an influent with low phosphate concentration (34.0 mg P·L-1) was fed to the crystallization plant; and period II, in which an influent with higher phosphate concentration (68.0 mg P·L-1) was used. A high efficiency of phosphorus recovery by struvite crystallization was obtained, even when the effluent treated had a high level of alkalinity. Phosphorus recovery percentage was around 77%, with a phosphate concentration in the effluent between 10.0 and 30.0 mg P·L-1. The experiments gained struvite pellets of 0.5-5.0 mm size. Moreover, the consumption of Mg(OH)2 was estimated at 1.5 mol Mg added·mol P recovered-1. Thus, industrial grade Mg(OH)2 can be an economical alternative as magnesium and alkali sources for struvite crystallization at industrial scale.

Characterization and biological abatement of diffuse methane emissions and odour in an innovative wastewater treatment plant.

An innovative and patented process for medium-high strength sewage which comprises an anaerobic step followed by a hybrid anoxic–aerobic chamber and a final ultrafiltration stage was characterized in terms of methane fugitive emissions as well as odours. The operation at ambient temperature implies higher methane content in the liquid anaerobic effluent, which finally causes concentrations around 0.01–2.4% in the off-gas released in the anoxic–aerobic chamber (1.25% average). Mass balances indicate that these emissions account for up to 30–35% of the total methane generated in the anaerobic reactor. A conventional biofilter (BF) operated at an empty bed residence time of 4 min was used to treat these emissions for 70 d. In spite of the fluctuations in the methane inlet concentrations derived from the operation of the wastewater treatment plant (WWTP), it was possible to operate at pseudo-steady-state conditions, achieving average removal efficiencies of 76.5% and maximum elimination capacities of 30.1 g m−3 h−1. Odour removal was quantified as 99.1%. Fluorescence in situ hybridization probes as well as metabolic activity assays demonstrated the suitability of the biomass developed in the WWTP as inoculum to start up the BF due to the presence of methanotrophic bacteria.

An innovative wastewater treatment technology based on UASB and IFAS for cost-efficient macro and micropollutant removal

An innovative process based on the combination of a UASB reactor and an IFAS system is proposed in order to combine different redox conditions and biomass conformations to promote a high microbial diversity. The objective of this configuration is to enhance the biological removal of organic micropollutants (OMPs) as well as to achieve the abatement of nitrogen by using the dissolved methane as an inexpensive electron donor. Results showed high removals of COD (93%) and dissolved methane present in the UASB effluent (up to 85%) was biodegraded by a consortium of aerobic methanotrophs and heterotrophic denitrifiers. Total nitrogen removal decreased slightly along the operation (from 44 to 33%), depending on the availability of electron donor, biomass concentration, and configuration (floccules and biofilm). A high removal was achieved in the hybrid system (>80%) for 6 of the studied OMPs. Sulfamethoxazole, trimethoprim, naproxen, and estradiol were readily biotransformed under anaerobic conditions, whereas ibuprofen or bisphenol A were removed in the anoxic-aerobic compartment. Evidence of the cometabolic biotransformation of OMPs has been found, such as the influence of nitrification activity on the removal of bisphenol A, and of the denitrification activity on ethinylestradiol removal.