High-rate nitrification of saline wastewaters using fixed-bed reactors.

Fixed-bed reactor (FBR) is a promising technology for realising robust high-rate nitrification. Only a few studies have investigated the effect of salinity on these systems. In this research work, the effect of gradual stepwise increase in chloride concentration (NaCl content) on the performance of high-rate nitrifying FBRs was studied at loading rates of about 1 kg NH4+-N∙m-3∙d-1 at 25 °C. Two lab-scale FBRs having stable biofilms (adapted to 4 g Cl-/L) grown on commercial media - plastic carrier fed with nanofiltration (NF) permeate of a landfill leachate concentrate, and clay beads fed with synthetic saline wastewater, respectively - were operated using up-flow velocities (u) of about 12 and 8 m/h, respectively, for a period of about 100 days, wherein the chloride content of the feed water was increased from 4 to 16 g/L (electrical conductivity: 13-45 mS/cm). On an average, the FBR packed with plastic carriers (u ≈ 12 m/h) offered ammonia removal percentages greater than 97%, whereas the FBR filled with clay beads due to its low bed porosity (and therefore, u ≈ 8 m/h only) gave nitrification efficiencies of about 70% only. The organic compounds contained in the NF permeate were found to temporarily inhibit the nitrifiers (causing nitrite accumulation), whereas the ammonia removed in the clay beads-packed FBR was transformed almost entirely into nitrate. Increase in chloride content did not have any observable detrimental effect on the performance of the reactors.

Pretreatment of Wastewater from Licorice Processing-A Preliminary Evaluation.

This study was performed as a preliminary investigation of anaerobic digestion and the activated sludge process as pretreatment options for highly loaded wastewater from licorice processing (approximately 8000 mg COD/L). Only 15% reduction of initial chemical oxygen demand (COD) was achieved by anaerobic digestion, whereas up to 80% reduction was attained with activated sludge process. Adsorption using powdered activated carbon (PAC) was studied for the removal of color and residual organics from the effluent of aerobic treatment. The combination of aerobic biological treatment with activated carbon adsorption offers a high-quality effluent, however only at very high carbon dosage (>2 kg PAC/m3).

Measured and predicted environmental concentrations of carbamazepine, diclofenac, and metoprolol in small and medium rivers in northern Germany.

This study evaluated the impact of secondary municipal effluent discharge on carbamazepine, diclofenac, and metoprolol concentrations in small and medium rivers in northern Germany and compared the measured environmental concentrations (MECs) to the predicted environmental concentrations (PECs) calculated with four well-established models. During a 1-year sampling period, secondary effluent grab samples were collected at four wastewater treatment plants (WWTPs) together with grab samples from the receiving waters upstream and downstream from the wastewater discharge points. The carbamazepine, diclofenac, and metoprolol concentrations were analyzed with high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS-MS) after solid phase extraction. In the secondary effluents, 84-790 ng/L carbamazepine, 395-2100 ng/L diclofenac, and 745-5000 ng/L metoprolol were detected. The carbamazepine, diclofenac, and metoprolol concentrations analyzed in the rivers downstream from the secondary effluent discharge sites ranged from <5 to 68, 370, and 520 ng/L, respectively. Most of the downstream pharmaceutical concentrations were markedly higher than the corresponding upstream concentrations. The impact of wastewater discharge on the MECs in rivers downstream from the WWTPs was clearly demonstrated, but the correlations of the MECs with dilution factors were poor. The smallest rivers exhibited the largest maximum MECs and the widest ranges of MECs downstream from the wastewater discharge point. Three of the four tested models were conservative, as they showed higher PECs than the MECs in the rivers downstream from the WWTPs. However, the most detailed model underestimated the diclofenac concentrations.

Removal of emerging micropollutants from nanofiltration retentate of municipal wastewater within biological fixed-bed reactors under nitrifying and denitrifying conditions.

Municipal water resource recovery facilities are not designed to eliminate micropollutants, leading to many pollutants entering the aquatic environment. Within this study, as part of the project MicroStop, the biological treatment of nanofiltration effluent (retentate) under pure aerobic (without nitrification) as well as nitrifying and denitrifying conditions has been investigated for micropollutant elimination. A potential of further biotransformation under increased hydraulic retention time (HRT) of 14 days was shown. Under both HRT of 7 and 14 days, eliminations below LOQ were achieved in the aerated bioreactor for gabapentin, iomeprol, and metoprolol, reaching > 95%, > 69 to > 92%, and > 72%, respectively. The reduction of diclofenac was positively influenced by longer HRT leading to an elimination of up to 67%. Sulfamethoxazole was reduced under denitrification, but accumulated under aeration, resulting in fluctuating results and an overall elimination of 78% under 14 days HRT. PRACTITIONER POINTS: The micropollutant elimination in fixed-bed bioreactors of highly concentrated nanofiltration retentate was studied. Pure aerobic (without nitrification), nitrifying, and denitrifying conditions were investigated under hydraulic retention times (HRT) of 7 and 14 days. Higher initial pollutant concentrations enhanced the biological degradability in attached growth for substances being moderately degradable in activated sludge systems. 4A potential of further biological micropollutant elimination was shown for gabapentin, iomeprol, metoprolol, and diclofenac.

Resources and nutrients oriented greywater treatment for non-potable reuses.

This paper evaluated the performance and suitability of a resources and nutrients oriented decentralized greywater treatment system which uses a submerged spiral wound module. This greywater treatment system is aimed at treating and recovering the resources present in the wastewater. The study revealed that the UF membrane filtration system was able to maintain a permeate flux between 6 and 10 L/m2/h. TOC can be reduced from the influent value of 161 to 28.6 mg/L in the permeate, meaning an average elimination rate of 83.4%. In addition, soluble nutrients such as ammonia and phosphorus can pass through the UF membrane and remain in the permeate. The total nitrogen and total phosphorus in the permeate were 16.7 and 6.7 mg/L respectively. The permeate was low in turbidity (below 1 NTU) and free of suspended solids and E. coli and had an excellent physical appearance. The permeate can be used in gardening and agriculture for irrigation and soil fertilization or alternatively for toilet flushing after disinfection. The retentate generated in this system can be treated with blackwater and kitchen waste in an anaerobic digester at a later stage for producing biogas or compost.

Comparison of NF-RO and RO-NF for the Treatment of Mature Landfill Leachates: A Guide for Landfill Operators.

Reverse osmosis (RO) and nanofiltration (NF) are among the state-of-the-art technologies for treating landfill leachates. Due to the complexity and variance in the composition of leachates, numerous combinations of multiple technologies are used for their treatment. One process chain for the treatment of raw leachate is RO followed by further concentration of RO-retentate using NF (RO-NF scheme). The aptness of this process train used by some landfill sites around the world (usually with the aim of volume reduction so as to re-inject the concentrate into the landfill) is questionable. This study investigated two schemes RO-NF and NF-RO (nanofiltration of raw leachate followed by reverse osmosis of NF permeate) to identify their merits/demerits. Experiments were conducted in bench scale using commercial membranes: DOW Filmtec NF270 and SW30HR. Filtration trials were performed at different pressures to compare the water and solute transports in the individual stages of the two schemes. Based on the water fluxes and compositions of retentates and permeates; osmotic pressures, energy demands, and other possible operational advantages were discussed. NF-RO offers some advantages and flexibility for leachate treatment besides being energy efficient compared to RO-NF, wherein osmotic pressure steadily increases during operation in turn increasing operation and maintenance costs.

Anaerobic digestion potential for ecological and decentralised sanitation in urban areas.

The potential of anaerobic digestion in ecological and decentralised sanitation has been investigated in this research. Different anaerobic digestion systems were proposed for the treatment of sewage, grey water, black water and faeces. Moreover, mathematical models based on anaerobic digestion model no.1 (ADM1) were developed for determination of a suitable design for each system. For stable performance of an upflow anaerobic sludge blanket (UASB) reactor treating sewage, the model results indicated that optimisation of wastewater conversion to biogas (not COD removal) should be selected for determination of the hydraulic retention time (HRT) of the reactor. For the treatment of sewage or black water in a UASB septic-tank, the model results showed that the sludge removal period was the main parameter for determination of the HRT. At such HRT, both COD removal and wastewater conversion are also optimised. The model results demonstrated that for treatment of faeces in an accumulation (AC) system at temperature > or = 25 degrees C, the filling period of the system should be higher than 60 days. For maximisation of the net biogas production (i.e. reduction of biogas losses as dissolved in the effluent), the separation between grey water, urine and faeces and reduction of water consumption for faeces flushing are required. Furthermore, the faeces and kitchen organic wastes and grey water are digested in, respectively, an AC system and UASB reactor, while the urine is stored.

Absorption of odourous substances using selective gas-liquid separation processes.

Absorption is one of the most widely used techniques for treating odourous waste gases. An improvement of the effectiveness of gas scrubbers can be achieved by using adapted washing liquids. A screening test is proposed as a low cost tool for testing washing liquids on industrial waste gases. The odour index is used to identify the main cause of the specific smell and to simplify the analysis of absorptive performances of washing liquids. The method is verified by experiments at a chocolate factory and a fat and oil refinery.