M. Soto

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 new device for measurement and control of gas production by bench scale anaerobic digesters

Abstract On the basis of an analysis, in terms of desirable characteristics and main sources of error, of existing apparatus for measuring biogas production by laboratory anaerobic digesters, we have developed a new device that is precise, inexpensive, easily constructed and capable of functioning autonomously for long periods. A slightly costlier version suitable for use in automatic control systems is also described.

BIODEGRADABILITY AND TOXICITY IN THE ANAEROBIC TREATMENT OF FISH CANNING WASTEWATERS

Abstract Sea fish canning industries produce effluents with a high load of organic matter. High concentrations of salts and possible production of H, S and NH4 + from the degradation of sulphates and proteins respectively, can cause toxicity/inhibition problems during the treatment of these effluents by anaerobic digestion. Biodegradability, toxicity/inhibition, operational temperatures, and the options of treating several effluents separately or jointly were studied. Anaerobic biodegradability reached up to 90% of soluble COD. Despite the high levels of sodium, ammonia and sulphide present, the results obtained allowus to predict a successful operation when adequate conditions are established. In order to gather more information as to the design of an industrial plant, complementary studies of pretreatment of effluents from fish meal factories and the use of high rate anaerobic digesters are proposed.

Semi‐micro C.O.D. determination method for high‐salinity wastewater

Abstract Semi‐micro determinations of the COD of wastewaters can err considerably if chloride is present. This article reports the degree to which accuracy is influenced by 1) COD itself; 2) the concentration of the masking agent HgSO4 in the digesting solution; 3) the presence of other salts, which is especially relevant in the case of water of marine origin; and 4) some of the other particular characteristics of the wastewater. Various experimental conditions are recommended for determination of the COD of different kinds of wastewater.

Sludge Granulation in UASB Digesters Treating Low Strength Wastewaters at Mesophilic and Psychrophilic Temperatures

This work reports a comparative study of the granulation process during the start-up of UASB digesters treating a diluted wastewater (500 mg COD l−1 as sucrose) at mesophilic (30°C) and psychrophilic (20°C) temperatures. The results show that the granulation process follows a similar pattern at both temperatures, complete granulation being achieved between 1 and 2 months from the start-up, at upflow superficial liquid velocities of 0.05 to 0.15 m h−1 and hydraulic retention times (HRT) of 6 to 3h. The UASB systems showed excellent stability and high treatment efficiency at HRT of 2h and organic loading rate (OLR) of 6 kg COD m−3 d−1, the percent COD removals being 95% (30°C) and 92% (20°C), while the percent COD converted to methane reached 67% (30°C) and 48% (20°C). The digester operated at 20°C maintained similar efficiencies when the OLR was increased up to 9 kg COD m−3 d−1, at an HRT of only 1.3h. The developed granules were similar in shape and size (2 to 3mm diameter), although different microbial m...

Characteristics and anaerobic treatability of municipal and industrial estate wastewaters

Centralised treatment of domestic sewage coming from A Coruña city (250000 inhabitants) and several medium and small size villages (up to 15000 inhabitants) together with industrial estate effluents was planned. The area population is about 380000 inhabitants and the overall effluent will reach about 600000 equivalent inhabitants. The characteristics of different streams will determine the treatment alternatives and pre-treatment requirements for individual streams. Domestic sewage from A Coruña showed medium to high organic content (741 mg l-1 of COD), while domestic sewage from small villages (Lorbé, Oleiros) and industrial estates (Sabón, A Grela) showed a high variability in organic content, with COD concentration ranging from 100 to 4000 mg l-1 or more. About 50-65% COD corresponded to suspended solids, although some industrial effluents showed lower values. Characterized industrial effluents had lower concentration of nutrients (nitrogen and phosphorus) and higher concentration of sulphate and alkalinity than domestic sewage. Anaerobic biodegradability was about 80% for domestic sewage, and ranged from 20 to 100% for industrial estate effluents. Furthermore, some industrial streams showed high microbial toxicity. The results indicate that anaerobic treatment of these effluents is of interest. However, specific pre-treatment for some individual streams or the adoption of minimisation and prevention measures in order to reach total or partial detoxification is suggested.