Municipal wastewater treatment by biofiltration: comparisons of various treatment layouts. Part 2: assessment of the operating costs in optimal conditions

This work aims to compare the operation costs (energy, reagents, waste management) for the three layouts usually used in wastewater treatment plants incorporating biofilters, using technical and economical data acquired during 10 years of operation of a Parisian plant (Seine Centre, 240,000 m(3) d(-1) -800,000 equivalent inhabitants). The final objective is to establish general economical data and tendencies that can be translated from our study to any biofiltration plant. Our results evidenced the savings achieved through the treatment process combining upstream and downstream denitrification. To use this layout reduced the operating costs by some 10% as compared with conventional processing only comprising downstream denitrification. Operating costs were respectively estimated at 37 and 34 €/1,000 m(3) for downstream denitrification and combining upstream and downstream denitrification layouts.     

Performance evaluation of the BioCAST technology: a new multi-zone wastewater treatment system

A new wastewater treatment technology, called BioCAST, has been designed and developed for high rate and simultaneous removal of organic carbonaceous compounds as well as nitrogen and phosphorus, along with reduced sludge generation. The treatment system has two interlinked reactors containing four independent zones with different environmental conditions of aerobic, microaerophilic, anoxic and anaerobic for the biological treatment of wastewater, as well as two clarification zones and a filtration unit for solid-liquid separation. The treatment system contains suspended as well as fixed-film microorganisms. The performance evaluation of the BioCAST system was carried out at organic loading rates of 0.95 to 1.86 kg/m(3) d, and nitrogen and phosphorus loading rates of 0.02 to 0.08 kg/m(3) d and 0.014 to 0.02 kg/m(3) d, respectively. The results demonstrated high removal efficiencies of carbon and nitrogen throughout the operation period, reaching 98.9 and 98.3%, respectively. Phosphorus removal efficiency was lower than 50% during the first 160 days of operation but it increased with the increase of nitrogen loading rate above 0.05 kg/m(3) day and concomitant reduction of C/N ratio below 15. Phosphorus removal efficiency reached 94.1%, producing an effluent concentration of 1.4 mg/L after 225 days of operation. The overall biomass yield based on the consumed COD was 3.7%.     

Enhanced denitrification with external carbon sources in a biological anoxic filter

Three parallel biological anoxic filters (BaFs) were operated to investigate the denitrification kinetics of methanol, brewery wastewater and bakery wastewater. The experiment was conducted within the temperature range of 15-20 °C, with an influent nitrate and carbon dosage of 30 mg/L and 150 mg COD/L (COD: chemical oxygen demand). The denitrification efficiencies of brewery wastewater, bakery wastewater and methanol were 84, 66 and 74%, specific denitrification rates were 1.44, 1.11 and 1.24 kg NO(3)-N/m(3) d, and total nitrogen (TN) removal rates were 74, 62 and 66%, respectively. The volatile attached solid (VAS) tests reveal that methanol has the minimum net biomass yield, so it needs the least carbon to nitrogen (expressed in COD to nitrate, C/N) ratio for complete denitrification. While the brewery wastewater and bakery wastewater need higher C/N ratio to remove all nitrate nitrogen, and they both may need pretreatment to remove phosphate when used as external carbon sources.     

Onsite wastewater nitrogen reduction with expanded media and elemental sulfur biofiltration

A passive biofiltration process has been developed to enhance nitrogen removal from onsite sanitation water. The system employs an initial unsaturated vertical flow biofilter with expanded clay media (nitrification), followed in series by a horizontal saturated biofilter for denitrification containing elemental sulfur media as electron donor. A small-scale prototype was operated continuously over eight months on primary wastewater effluent with total nitrogen (TN) of 72.2 mg/L. The average hydraulic loading to the unsaturated biofilter surface was 11.9 cm/day, applied at a 30 min dosing cycle. Average effluent TN was 2.6 mg/L and average TN reduction efficiency was 96.2%. Effluent nitrogen was 1.7 mg/L as organic N, 0.93 mg/L as ammonium (NH(4)-N), and 0.03 as oxidized (NO(3) + NO(2)) N. There was no surface clogging of unsaturated media, nitrate breakthrough, or replenishment of sulfur media over eight months. Visual and microscopic examinations revealed substantially open pores with limited material accumulation on the upper surface of the unsaturated media. Material accumulation was observed at the inlet zone of the denitrification biofilter, and sulfur media exhibited surface cavities consistent with oxidative dissolution. Two-stage biofiltration is a simple and resilient system for achieving high nitrogen reductions in onsite wastewater.     

Anaerobic co-digestion of sludge with other organic wastes and phosphorus reclamation in wastewater treatment plants for biological nutrients removal.

This paper deals with the performances obtained in full scale anaerobic digesters co-digesting waste activated sludge from biological nutrients removal wastewater treatment plants, together with different types of organic wastes (solid and liquid). Results showed that the biogas production can be increased from 4000 to some 18,000 m3 per month when treating some 3-5 tons per day of organic municipal solid waste together with waste activated sludge. On the other hand, the specific biogas production was improved, passing from 0.3 to 0.5 m3 per kgVS fed the reactor, when treating liquid effluents from cheese factories. The addition of the co-substrates gave minimal increases in the organic loading rate while the hydraulic retention time remained constant. Further, the potentiality of the struvite crystallisation process for treating anaerobic supernatant rich in nitrogen and phosphorus was studied: 80% removal of phosphorus was observed in all the tested conditions. In conclusion, a possible layout is proposed for designing or upgrading wastewater treatment plants for biological nutrients removal process.     

Aeration effect on the efficiency of swine manure treatment in a trickling filter packed with organic materials.

Effect of aeration rate on the removal of organic matter and nitrogen and on the formation of NH3, N2O and N2 was studied for an extensive biofiltration system packed with an organic media, which was used to treat pig manure. The results show high removal of BOD5 and TSS (99 and > or = 98%), independently of the four aeration rate tested (3.4-34 m3/m2 x h). Aeration rate > or = 4.4 m/h resulted in high ammonia stripping during start-up (> or = 1.0 kg NH3-N/m3 of swine manure treated), while using 3.4 m/h only 0.3 kg NH3-N/m3 were stripped. Complete nitrification was achieved after day 100 of operation, except in the biofilter with the lowest aeration rate. Simultaneous denitrification established in all the biofilters. Applying an aeration rate of 9.4 m/h up to 1.2 kg nitrogen was removed in the form of N2 for each m3 of swine manure treated. Contrary to the expectations, N2 formation and release increased with the aeration rate. This particular behaviour seems to be related to the punctual accumulation of water layers inside the biofilters, caused by the air force flowing in the opposite direction to the water flux. N2O production was quite similar in all biofilters (between 0.25-0.36 kg N2O-N/m3 of swine manure treated).     

Hydrogen limitation--a method for controlling the performance of membrane biofilm reactor for autotrophic denitrification of wastewater.

Hydrogen-driven denitrification using the fiber membrane biofilm reactor (MBfR) was evaluated for consistent operation in tertiary wastewater treatment. The possibility of controlling the process rates, as well as biofilm parameters by supplying limited amounts of electron donor (hydrogen), was tested. Limiting the hydrogen supply proved to be efficient in controlling the biofilm growth and performance of the MBfR. Denitrification rates remained unchanged for both synthetic wastewater (SWW) and real municipal wastewater (MWW) effluent as well through the fluctuations in the substrate (NO3-N) concentration. The average denitrification rates were 0.50 (+/- 0.02) g NO3-N per day per m2 for SWW and 0.59 (+/- 0.04) g NO3-N per day per m2 for MWW. Biofilm density rather than thickness was the determining factor in substrate diffusion and biofilm sloughing, ultimately determining operating stability. Limited hydrogen supply assured constant volatile solids (VS) concentration in the biofilm. It was determined that VS/TS ratio higher than 0.25 assured stable biofilm operation. Decrease of VS/TS ratio below 0.25 led to shearing of the nonbiological outer layers of the biofilm. The values of chemical oxygen demand (COD), volatile suspended solids (VSS) and total suspended solids (TSS) in the final effluent were stable and well below wastewater effluent guidelines. Substitutions of bicarbonate with gaseous carbon dioxide as the carbon source did not affect denitrification rates despite lower than optimum pH conditions.     

Comparing cost and process performance of activated sludge (AS) and biological aerated filters (BAF) over ten years of full sale operation.

In the early 1990s, the Wastewater Treatment Plant (WWTP) of Frederikshavn, Denmark, was extended to meet new requirements for nutrient removal (8 mg/L TN, 1.5 mg TP/L) as well as to increase its average daily flow to 16,500 m(3)/d (4.5 MGD). As the most economical upgrade of the existing activated sludge (AS) plant, a parallel biological aerated filter (BAF) was selected, and started up in 1995. Running two full scale processes in parallel for over ten years on the same wastewater and treatment objectives enabled a direct comparison in relation to operating performance, costs and experience. Common pretreatment consists of screening, an aerated grit and grease removal and three primary settlers with chemical addition. The effluent is then pumped to the two parallel biological treatment stages, AS with recirculation and an upflow BAF with floating media. The wastewater is a mixture of industrial and domestic wastewater, with a dominant discharge of fish processing effluent which can amount to 50% of the flow. The maximum hydraulic load on the pretreatment section as a whole is 1,530 m(3)/h. Approximately 60% of the sewer system is combined with a total of 32 overflow structures. To avoid the direct discharge of combined sewer overflows into the receiving waters, the total hydraulic wet weather capacity of the plant is increased to 4,330 m(3)/h, or 6 times average flow. During rain, some of the raw sewage can be directed through a stormwater bypass to the BAF, which can be modified in its operation to accommodate various treatment needs: either using simultaneous nitrification/denitrification in all filters with recirculation introducing bottom aeration with full nitrification in some filters for storm treatment and/or post-denitrification in one filter. After treatment, the wastewater is discharged to the Baltic Sea through a 500 m outfall. The BAF backwash sludge, approximately 1,900 m(3) per 24 h in dry weather, is redirected to the AS plant. Primary settler sludge and the combined biosolids from the AS plant are anaerobically digested, with methane gas being used for generation of heat and power. On-line measurements for the parameters NO3, NO2, NH4, temperature as well as dissolved oxygen (DO) are used for control of aeration and external carbon source (methanol). Dosing of flocculants for P-removal is carried out based on laboratory analysis and jar tests. This paper discusses the experience gained from the plant operation during the last ten years, compiling comparative performance and cost data of the two processes, as well as their optimisation.     

Integrated natural treatment systems for developing communities: low-tech N-removal through the fluctuating microbial pathways.

Integration of natural treatment systems (NTS) (WSP, wetlands etc.) with each other as well as with advanced unit processes (biofiltration) offers a second lease of life to NTS. Long-term full and pilot cale experience in South Africa and Thailand have shown that contrary to a common view, a low tech N-removal from municipal and light industrial wastewater is a reality for a developing community The high treatment efficiency is ascribed to interplay of N-related processes complementing each other. The present FISH-based (Fluorescence In Situ Hybridization) approach to microbial community structure is a pioneering effort in the field of NTS. It establishes interrelationships between major N-removing groups (aerobic and anaerobic ammonia oxidizers (ANAMMOX), denitrifiers) within integrated systems and links them to the high treatment performance. Seasonally fluctuating presence of the ANAMMOX bacteria (0-2.5% of total bacterial numbers) in the NTS (free surface flow wetland) is reported for the first time. Their numbers correlate with metabolically dependent ammonia-oxidizers (2.0-3.0%) but not with stable overall Planctomycetes population (4.5-5.1%). As a result of the flexible microbial structure the robust low cost removal down to TN < 10 mg/L is routinely feasible at the loading rates ranging from 0.005 to 0.08 TN kg/m3/day.     

Removal of alkylphenols and polybromodiphenylethers by a biofiltration treatment plant during dry and wet-weather periods

This paper investigates the occurrence of alkylphenols (APs) and polybromodiphenylethers (PBDEs) in raw wastewater during dry and wet-weather periods, and their removal by physico-chemical lamellar settling and biofiltration techniques. Due to in-sewer deposit erosion and, to a lesser extent, to external inputs, raw effluents exhibit from 1.5 to 5 times higher AP and PBDE concentrations during wet periods compared with dry ones. The lamellar settler obtains high removal of APs and PBDEs under both dry and wet-weather flows (>53% for Σ(6)AP and >89% for Σ(4)PBDE), confirming the insensitivity of this technique to varying influent conditions. Indeed, despite the higher pollutant concentrations observed in raw effluents under wet-weather flows, adjusting the addition of coagulant-flocculent allows for efficient removal. By combining physical and biological processes, the biofiltration unit treats nutrient pollution, as well as Σ(6)AP and Σ(4)PBDE contamination (58 ± 5% and 75 ± 6% respectively). Although the operating conditions of the biofiltration unit are modified during wet periods, the performance in nutrient pollution, APs and light PBDE congeners remains high. Nevertheless, lower efficiency has been noted in nitrogen pollution, i.e. no denitrification occurs, and BDE-209 (not removed during wet-weather periods). In conclusion, this study demonstrates that the combination of both techniques treats AP and PBDE pollution efficiently during dry periods, but that they are also suitable for stormwater treatment.     

Electron beam treatment of textile dyeing wastewater: operation of pilot plant and industrial plant construction.

A pilot plant for treating 1000 m3/day of dyeing wastewater with e-beam has been constructed and operated since 1998 in Daegu, Korea together with the biological treatment facility. The wastewater from various stages of the existing purification process has been treated with an electron beam in this plant, and it gave rise to elaborating the optimal technology of the electron beam treatment of wastewater with increased reliability for instant changes in the composition of wastewater. Installation of the e-beam pilot plant resulted in decolorizing and destructive oxidation of organic impurities in wastewater, appreciable reduction of chemical reagent consumption, in reduction of the treatment time, and in increase in the flow rate limit of existing facilities by 30-40%. Industrial plant for treating 10,000 m3/day each, based upon the pilot experimental result, is under construction and will be finished by 2005. This project is supported by the International Atomic Energy Agency (IAEA) and Korean Government.     

Use of immobilised bacteria for the wastewater treatment--examples from the sugar industry.

This work focuses on the implementation of high performance systems to the wastewater treatment of sugar factories. For this purpose, systems with immobilised bacteria were studied. For the hydrolysis of organic matter and denitrification, fluidized bed reactors were used. The nitrification was studied with an airlift reactor system. Both hydrolysis and nitrogen elimination were investigated on laboratory and pilot scales in sugar factories. Although with porous materials higher biomass concentrations are attainable for the hydrolysis (up to 55 kg/m3), for economical reasons sand was used (22.5 kg/m3) for the pilot scale-study. With a pilot-scale reactor (volume 1 m3) the maximum sucrose conversion rate achieved with sand in the first campaign was 52 kg/(m3 d). For the nitrogen elimination on the pilot scale, a system with denitrification and nitrification was combined. The highest performance for the nitrification (reactor volume: 0.68 m3) with pumice as support material was 1.2 kg NH4-N/(m3 d), limiting the whole system. The denitrification rate (reactor volume: 0.12 m3) was four times higher (3.5-5 kg NO3-N/(m3 d). Rules of the modelling of the system are discussed.     

Anaerobic treatment of a medium strength industrial wastewater at low-temperature and short hydraulic retention time: a pilot-scale experience

The aim of this work was to evaluate the performance of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of cereal-processing industry wastewater under low-temperature conditions (17 degrees C) for more than 300 days. The applied organic loading rate (OLR(appl)) was gradually increased from 4 to 6 and 8 kg COD(sol)/m3d by increasing the influent soluble chemical oxygen demand (COD(sol)), while keeping the hydraulic retention time constant (5.2 h). The removal efficiency was high (82 to 92%) and slightly decreased after increasing the influent COD(sol) and the OLR(appl). The highest removed organic loading rate (OLR(rem)) was reached when the UASB reactor was operated at 8 kg COD(sol)/m3d and it was two times higher than that obtained for an OLR(appl) of 4 kg COD(sol)/m3d. Some disturbances were observed during the experimentation. The formation of biogas pockets in the sludge bed significantly complicated the biogas production quantification, but did not affect the reactor performance. The volatile fatty acids in the effluent were low, but increased as the OLR(appl) increased, which caused an increment of the effluent COD(sol). Anaerobic treatment at low temperature was a good option for the biological pre-treatment of cereal processing industry wastewater.     

Production integrated treatment of textile wastewater by closing raw material cycles.

A method for the in-house treatment of partial wastewater flows and the recycling of treated process water into the textile finishing process was developed in order to recycle effluents from textile finishing industry and feed them back into the production process. The method is based on a two-stage biological anaerobic-aerobic process to split colouring wastewater agents and to degrade organic substances contained in the water as well as a chemical stage to remove the remaining color of the water with the help of ozone. In the framework of a research and development project a demonstration plant for a treatment capacity of 1440 m3 per working day was installed and started in a textile finishing company. At the plant, a wastewater flow and a recycling flow are treated separately in two different treatment lanes. Approximately 40% of the total wastewater flows, i.e. 576 m3/d are treated in the wastewater lane, and a maximum of 60% of total wastewater, i.e. 864 m3/d are treated in the recycling lane. Thanks to the preliminary treatment of wastewater flows, which are discharged into the municipal sewage works, a reduction of average COD levels in the sewage works effluents could be achieved.     

External carbon feeding strategy for enhancing nitrogen removal in SBR.

Effective method for feeding an external carbon source (ECS) in SBR was investigated to enhance denitrification based on modifying the anoxic/aerobic sub-cycle for swine wastewater treatment. The wastewater discharged from the scraper-type barns contains relatively low readily biodegradable organic. Therefore NOx-N was accumulated during repeating sub-cycle in SBR operation. When acetic acid was fed as ECS during the final sub-cycle, the maximum nitrogen removal rate was 0.22 kg N/m3/d. This was due to both less denitrification rate during the sub-cycle period and inhibition of denitrification by pH drop during the final cycle. The pH drop was caused by a large amount of ECS feeding to remove high concentration of NOx-N in the final period. To overcome these limitations and achieve higher nitrogen removal rate, the intermittent ECS feeding method with raw wastewater at every anoxic period was developed. Using the modifying ECS feeding method, the removal rate was increased to 0.45 kg N/m3/d without NOx-N accumulation.     

Utilization of a hybrid sequencing batch reactor (HSBR) as a decentralized system of domestic wastewater treatment

This paper presents the experiments carried out in a hybrid sequencing batch reactor (HSBR), used for biological treatment of sewage. The HSBR was built in a cylindrical shape and made of stainless steel, with a volume of 1.42 m3. Besides the biomass in suspension, the reactor also carried fixed biomass (hybrid process), adhered in the support material. This consisted of a nylon net disposed in a grille for biofilm biomass adhesion. The reactor worked fully automated in operational cycles of maximum 8 hours each, presenting the following phases: filling, anoxic, aerobic, settle and draw of treated effluent, with 3 fillings per cycle. Increasing organic loads (0.14 to 0.51 kg TCOD/m3 day) and ammonium loads (0.002 to 0.006 kg NH4-N/m3.day) were tested. We monitored the reactor's performance by measuring the liquid phase (COD, pH, temperature, DO, nitrogen and phosphorus) during the cycles and by measuring the sludge through respirometric tests. The results obtained demonstrated TCOD removal efficiency between 73 and 96%, and ammonium removal efficiency between 50 and 99%. At the end of the cycles, the effluent presented ammonium concentration <20 mg/L, meeting the Brazilian environmental legislation standards (CONAMA 357/2005) regarding discharges into the water bodies. Respirometric tests showed biomass dependency on FCOD concentrations. Results have demonstrated the potential of this type of reactor for decentralized treatment of domestic wastewater.     

Domestic wastewater treatment by a constructed wetland system planted with rice

The experiments were conducted in four concrete laboratory scale free water surface constructed wetland units 1 m wide, 1.5 m long and 0.8 m deep. Paddy field soil was added to a depth of 0.4 m and rice seedlings (Oryza sativa L.) were transplanted into the units at a density of 25 plants/m(2). Domestic wastewater collected from Chiang Mai University was applied into each unit via two different modes to evaluate suitable conditions for wastewater treatment and rice yield. In the first experiment, the wastewater was fed intermittently (7 h/day) with a hydraulic loading rate of 2, 4, 6 and 8 cm/day. The maximum removal efficiencies for chemical oxygen demand, biological oxygen demand, total kjedahl nitrogen and suspended solids were only 49.1, 58.7, 64.0 and 59.4%, respectively, due to the short hydraulic retention time for the biodegradation of organic substances. In the second experiment, the wastewater in each unit was inundated to a depth of 15 cm for 10, 15, 20 and 25 days in each unit and then drained and re-flooded. Removal efficiencies of chemical oxygen demand, biological oxygen demand, total kjedahl nitrogen and suspended solids were greater than in the first experiment especially at the 25 day retention time and except for suspended solids met the Thai national effluent standard. The study revealed that apart from wastewater treatment, wastewater can replace natural water to grow rice in the dry season or throughout the year. Moreover, nutrients in wastewater can be a substitute for chemical fertilizers. Rice grain production was 4,700 kg/ha and only 6% less than the production from the conventional paddy field.     

Innovations in wastewater treatment: the moving bed biofilm process.

This paper describes the moving bed biofilm reactor (MBBR) and presents applications of wastewater treatment processes in which this reactor is used. The MBBR processes have been extensively used for BOD/COD-removal, as well as for nitrification and denitrification in municipal and industrial wastewater treatment. This paper focuses on the municipal applications. The most frequent process combinations are presented and discussed. Basic design data obtained through research, as well as data from practical operation of various plants, are presented. It is demonstrated that the MBBR may be used in an extremely compact high-rate process (<1 h total HRT) for secondary treatment. Most European plants require P-removal and performance data from plants combining MBBR and chemical precipitation is presented. Likewise, data from plants in Italy and Switzerland that are implementing nitrification in addition to secondary treatment are presented. The results from three Norwegian plants that are using the so-called combined denitrification MBBR process are discussed. Nitrification rates as high as 1.2 g NH4-N/m2 d at complete nitrification were demonstrated in practical operation at low temperatures (11 degrees C), while denitrification rates were as high as 3.5g NO3-Nequiv./m2.d. Depending on the extent of pretreatment, the total HRT of the MBBR for N-removal will be in the range of 3 to 5 h.     

Characterization of bacterial biofilm communities in tertiary treatment processes for wastewater reclamation and reuse

The concern with wastewater reuse as a sustainable water resource in urban areas has been growing. For the reclamation and distribution of wastewater, biofilm development deserves careful attention from the point of view of its promotion (e.g. biofiltration) and inhibition (e.g. clogging and hygiene problems). As the first step to control biofilm development, bacterial biofilm communities in tertiary treatment processes were characterized by using molecular biological methods. The result of clone library analysis showed that Nitrospirae-related (nitrite-oxydizing bacteria) and Acidobacteria-related (probably oligotrophic bacteria) groups were dominant. The ratio of the Nitrospirae-related group to the Acidobacteria-related group was associated with ammonia load, whereas other operational conditions (process, media, temperature, salt) did not clearly affect the phylum-level community or the dominant sequence of nitrifying bacteria. The result of real-time PCR also indicated that high ammonia load promotes the proliferation of nitrite- and ammonia-oxidizing bacteria. Regarding water supply systems, some researchers also have suggested the dominance of Nitrospirae- and Acidobacteria-related groups in biofilm formed on water distribution pipes. In tertiary wastewater treatment, therefore, it is concluded that oligotrophic and autotrophic bacteria are the dominant groups in biofilm samples because assimilable organic carbon is too poor to proliferate various heterotrophic bacteria.     

Winery and distillery wastewater treatment by anaerobic digestion.

Anaerobic digestion is widely used for wastewater treatment, especially in the food industries. Generally after the anaerobic treatment there is an aerobic post-treatment in order to return the treated water to nature. Several technologies are applied for winery wastewater treatment. They are using free cells or flocs (anaerobic contact digesters, anaerobic sequencing batch reactors and anaerobic lagoons), anaerobic granules (Upflow Anaerobic Sludge Blanket--UASB), or biofilms on fixed support (anaerobic filter) or on mobile support as with the fluidised bed. Some technologies include two strategies, e.g. a sludge bed with anaerobic filter as in the hybrid digester. With winery wastewaters (as for vinasses from distilleries) the removal yield for anaerobic digestion is very high, up to 90-95% COD removal. The organic loads are between 5 and 15 kgCOD/m3 of digester/day. The biogas production is between 400 and 600 L per kg COD removed with 60 to 70% methane content. For anaerobic and aerobic post-treatment of vinasses in the Cognac region, REVICO company has 99.7% COD removal and the cost is 0.52 Euro/m3 of vinasses.