J.M. Lema

Characteristics of landfill leachates and alternatives for their treatment: A review

Sanitary landfilling is the most common way to eliminate solid urban wastes. An important problem associated to landfills is the production of leachates. The factors determining the characteristics of leachates from solid urban waste landfills are reviewed together with the reported compositions of leachates from various countries and origins. New data obtained from two landfills of different age in the same area are reported. The advantages and disadvantages of the various existing alternatives for solving the leachates problem are discussed under the items: (1) Leachate Channeling (Combined Treatment with domestic sewage, Recycling and Lagooning with recycling). (2) Biological Processing (Aerobic and Anaerobic). (3) Chemical/Physical Treatment (Chemical Precipitation, Chemical Oxidation, Adsorption onto activated carbon, Reverse osmosis, and Stripping of NH3). The performance at several operational conditions of the most important methods is reviewed and summarized in several tables. From all this information a table designed to aid the choice of solutions for each particular case is presented.

Removal of pharmaceutical and Personal Care Products (PPCPs) under nitrifying and denitrifying conditions.

The contribution of volatilization, sorption and transformation to the removal of 16 Pharmaceutical and Personal Care Products (PPCPs) in two lab-scale conventional activated sludge reactors, working under nitrifying (aerobic) and denitrifying (anoxic) conditions for more than 1.5 years, have been assessed. Pseudo-first order biological degradation rate constants (k(biol)) were calculated for the selected compounds in both reactors. Faster degradation kinetics were measured in the nitrifying reactor compared to the denitrifying system for the majority of PPCPs. Compounds could be classified according to their k(biol) into very highly (k(biol)>5Lg(SS)(-1)d(-1)), highly (1<k(biol)<5Lg(SS)(-1)d(-1)), moderately (0.5<k(biol)<1Lg(SS)(-1)d(-1)) and hardly (k(biol)<0.5Lg(SS)(-1)d(-1)) biodegradable. Results indicated that fluoxetine (FLX), natural estrogens (E1+E2) and musk fragrances (HHCB, AHTN and ADBI) were transformed to a large extent under aerobic (>75%) and anoxic (>65%) conditions, whereas naproxen (NPX), ethinylestradiol (EE2), roxithromycin (ROX) and erythromycin (ERY) were only significantly transformed in the aerobic reactor (>80%). The anti-depressant citalopram (CTL) was moderately biotransformed under both, aerobic and anoxic conditions (>60% and >40%, respectively). Some compounds, as carbamazepine (CBZ), diazepam (DZP), sulfamethoxazole (SMX) and trimethoprim (TMP), manifested high resistance to biological transformation. Solids Retention Time (SRT(aerobic) >50d and <50d; SRT(anoxic) >20d and <20d) had a slightly positive effect on the removal of FLX, NPX, CTL, EE2 and natural estrogens (increase in removal efficiencies <10%). Removal of diclofenac (DCF) in the aerobic reactor was positively affected by the development of nitrifying biomass and increased from 0% up to 74%. Similarly, efficient anoxic transformation of ibuprofen (75%) was observed after an adaptation period of 340d. Temperature (16-26 degrees C) only had a slight effect on the removal of CTL which increased in 4%.

Methanogenic and non-methanogenic activity tests. Theoretical basis and experimental set up

Abstract The theoretical basis of the methods allowing to determine and calculate methanogenic and non-methanogenic sludge activities in anaerobic digesters are examined and, accordingly, proper experimental conditions are established. Some operational parameters of batch experiments like initial substrate concentration and inoculum size can be estimated from the expected kinetic constants. Methods based on the theoretical considerations are proposed and employed in order to evaluate: (a) the maximum methanogenic activity of anaerobic digester sludges, (b) the maximum hydrolytic and acidogenic activities and (c) the kinetic parameters corresponding to methanogenic, acidogenic and hydrolytic steps. Results show that maximum methanogenic activity of sludges from anaerobic reactors may be determined accurately by using small vials connected to Mariotte flasks with an alkaline fluid. A different procedure based on head space gas chromatographic analysis was also evaluated. This method is suitable to determine very low methane productions and may be applied to the methanogenic activities determination at substrate concentrations lower than the half-saturation constant. The activity tests were advisable to determine either the specific microbial activity, expressed by a sole parameter (i.e. maximum specific activity); or the kinetic of substrate consumption, that implies data adjustment to the Monod or the Andrews Model for the calculation of maximum specific activity and half saturation constant. The developed methods were applied to characterize the biomass of a lab-scale mesophilic anaerobic filter.

A methodology for optimising feed composition for anaerobic co-digestion of agro-industrial wastes

An optimisation protocol for maximising methane production by anaerobic co-digestion of several wastes was carried out. A linear programming method was utilised to set up different blends aimed at maximising the total substrate biodegradation potential (L CH(4)/kg substrate) or the biokinetic potential (L CH(4)/kg substrate d). In order to validate the process, three agro-industrial wastes were considered: pig manure, tuna fish waste and biodiesel waste, and the results obtained were validated by experimental studies in discontinuous assays. The highest biodegradation potential (321 L CH(4)/kg COD) was reached with a mixture composed of 84% pig manure, 5% fish waste and 11% biodiesel waste, while the highest methane production rate (16.4 L CH(4)/kg COD d) was obtained by a mixture containing 88% pig manure, 4% fish waste and 8% biodiesel waste. Linear programming was proved to be a powerful, useful and easy-to-use tool to estimate methane production in co-digestion units where different substrates can be fed.

Influence of the content in fats and proteins on the anaerobic biodegradability of dairy wastewaters.

Abstract The relative amounts of fats, proteins and carbohydrates in wastewaters from dairy industries cause problems during their anaerobic treatment. The anaerobic biodegradability of two synthetic wastewaters, one rich in fats (chemical oxygen demand (COD) ratio; Fats/Proteins/Carbohydrates: 1.7/0.57/1) and the other with a low fat content (COD ratio; Fats/Proteins/Carbohydrates: 0.05/0.54/1) was studied in samples with total COD ranging from 0.4 to 20 g/l. There were no problems of sludge flotation and the maximum biodegradability and methanisation were obtained when operating with wastewaters in the range of 3–5 gCOD/l. The intermediates of fat degradation (glycerol and long chain fatty acids) seemed not to reach concentrations high enough to affect the process. The anaerobic biodegradation of fat-rich wastes was slower than carbohydrate-rich wastes due to the slower hydrolytic step of fat degradation which prevented the accumulation of volatile fatty acids (VFAs) and favoured the overall process. Carbohydrate-rich wastewater degradation produced free ammonia (FA) at concentrations near to inhibitory levels (62.2 mg FA/l), but in this case, ammonia production facilitated regulation of fall in pH caused by of the accumulation of VFA.

Sodium inhibition in the anaerobic digestion process: Antagonism and adaptation phenomena

Abstract The effect of sodium on the methanization of volatile fatty acid (VFA) mixtures was evaluated for three different sludges. Sodium concentrations causing 50% inhibition ranged from 3 to 16 g l −1 in the absence of nutrients or other salts, showing a higher tolerance to sodium in the sludges obtained from the digesters treating high saline wastewaters. This fact is considered to be a consequence of sludge adaptation to sodium. Furthermore, the adaptation of methanogenic bacteria to sodium was also found during the batch assays: After 40 days of digestion, two different sludges (subjected to 6.9 and 21.5 g Na + l −1 , respectively) increased the relative methanogenic activity from 0% to about 45% of the blank activity. The antagonism phenomena, due to the presence of cations and anions contained in the assayed media, greatly influenced the sodium effect on anaerobic sludges. Sodium concentrations causing 50% inhibition may be increased by 4 to 10 g l −1 or more when sea water is used instead of NaCl. Nutrients also influence the sodium toxicity. The effect of sodium in each step of the anaerobic digestion process appears to be different depending on the sludge. For an adapted sludge, sodium caused 50% inhibition of propionic, acetic and n -butyric utilizers at concentrations of 10.5, 17, and 19 g l −1 , respectively, an indication that propionic utilizers had less adaptation potential. These concentrations ranged between 5 and 6 g l −1 for an unadapted sludge. The methanization of a more complex substance, such as glucose, was less extensively affected than the methanization of VFA. Results from continuous assays agree with those obtained from batch assays.

Enzymatic pretreatment to enhance oil extraction from fruits and oilseeds : a review

Abstract Enzymatic treatment to enhance oil recovery from olive, avocado or coconut pastes has been used with excellent results both on a laboratory and industrial scale (olive) obtaining the oil in shorter times and increasing the capacity of the equipment. This treatment was tried for the extraction of oil and protein from oilseeds on a laboratory scale (peanut, rapeseed — also in a pilot plant — sunflower and soybean). Considering that two thirds of the total fat and oil production is supplied by oilseeds (soybean, sunflower, rape and palm accounting for more than 70% of vegetable oils) this is a promising field for biotechnological applications. In the present work the different processes, as well as the factors affecting their efficiency, are discussed.

Pre-treatment of hospital wastewater by coagulation-flocculation and flotation

Coagulation-flocculation and flotation processes were evaluated for the pre-treatment of hospital wastewater, including the removal of 13 pharmaceutical and personal care products (PPCPs). Coagulation-flocculation assays were performed in a Jar-Test device and in a continuous pilot-scale plant. Raw hospital wastewater as well as the effluent from the continuous coagulation plant were treated in a flotation cell. Removal of total suspended solids (TSS) during pre-treatment was very effective, reaching an average removal efficiency of 92% in the combined coagulation-flotation process. Musk fragrances were eliminated to a high degree during batch coagulation-flocculation (tonalide: 83.4+/-14.3%; galaxolide: 79.2+/-9.9%; celestolide: 77.7+/-16.8%), presumably due to their strong lipophilic character which promotes the interaction of these compounds with the lipid fraction of solids. For diclofenac (DCF), naproxen (NPX) and ibuprofen (IBP) maximum removals of 46%, 42% and 23%, respectively, were obtained, while the rest of PPCPs were not affected by the physico-chemical treatment. Flotation of raw wastewater led to slightly worse results compared to coagulation-flocculation, although the combined action of both improved the overall efficiency of the process. The proposed pre-treatment strategy for hospital wastewater is useful for assimilating its conventional physico-chemical characteristics to that of municipal wastewater as well as for reducing the load of some PPCPs into the sewer system.

Nitrification in saline wastewater with high ammonia concentration in an activated sludge unit

A nitrifying activated sludge reactor fed with a high salinity medium was operated efficiently at ammonia loading rates between 1 and 4 g NH4+ -N l(-1) d(-1). The system became completely inefficient at inlet salt concentrations higher than 525 mM due to the mixed inhibition effect of salts and ammonia. The final product was mainly nitrate although dissolved oxygen limitations caused sporadic ammonia and nitrite accumulations. Specific nitrifying activity decreased due to the saline effect. A set of activity tests showed that in the continuous reactor non-adapted biomass is rather more sensitive than biomass to the saline effect. Physical properties of biomass in the reactor (sludge volumetric index and zone settling velocity) were not affected by the saline concentration, a biomass concentration of 20 gVSS l(-1) was achieved.

Comparison of predicted and measured concentrations of selected pharmaceuticals, fragrances and hormones in Spanish sewage

A review of consumption and excretion rates of 17 pharmaceuticals, two musk fragrances and two hormones by the Spanish population in 2003 was performed. For that purpose, three different models were used: (i) extrapolation of the per capita use in Europe to the number of inhabitants of Spain for musk fragrances; (ii) annual prescription items multiplied by the average daily dose for pharmaceuticals and; (iii) excretion rates of different groups of population for hormones. This information enabled the prediction of the expected concentrations (PEC) entering sewage treatment plants (STPs), which were subsequently compared with the measured environmental concentrations (MEC) in raw sewage. Annual drugs consumption in Spain ranges from few kilograms (Oxazepam and 17alpha-ethinylestradiol) to several hundred of tons (Ibuprofen). The quantities of musks used accounts for 110-450 kg d(-1) and the total amount of hormones excreted daily reaches almost 1 kg d(-1). 12 out of 21 selected substances were predicted to be present in raw sewage influent at concentrations greater than 100 ng l(-1) and these predicted concentrations fitted with the measured values for half of them (Carbamazepine, Diazepam, Ibuprofen, Naproxen, Diclofenac, Sulfamethoxazole, Roxithromycin, Erythromycin and 17alpha-ethinylestradiol).