M.F. Colmenarejo

Production of biomass (algae-bacteria) by using a mixture of settled swine and sewage as substrate

This paper presents the use of a mixture of settled swine and sewage as substrate for biomass production, mainly constituted by microalgae Chlorella vulgaris and aerobic bacteria, growing outdoor at different dilution rates in a continuous mode. The experiments were carried out in 16-litre volume laboratory ponds operating at hydraulic retention times (HRT) in a range of 4–14 days equivalent to dilution rates (D) in a range of 0.250–0.071 d−1. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total biochemical oxygen demand (TBOD5), total suspended solids (TSS), volatile suspended solids (VSS), total Chlorophyll (Σ C), total Kjeldahl nitrogen (TKN), ammonia nitrogen, total phosphorous, orthophosphate and pH were monitored. An empirical relationship between the dilution rate (D) and the removal efficiencies of TCOD, SCOD, TBOD5, TKN and total phosphorous was found. The occurrence of an inhibition process for TCOD, TBOD5, TKN and total phosphorous removals was observed. The Andrews kinetic model was successfully applied to these experimental data, while the Monod model was more suitable for studying the variation of the SCOD removal rate with the effluent SCOD concentration. The maximum microalgal biomass productivity was found to be in the range of 93–98 mg VSSA/L d (37.2–39.2 g/m2d) at dilution rates in the range of 0.167–0.250 d−1, where VSSA is the concentration of microalgae expressed in VSS. In the case of the bacteria, the productivity increased linearly with the dilution rate being maximum at a D value of 0.25 d−1. It was concluded that the mixture of pre-treated swine and sewage used as substrate, contributed to the obtention of a high biomass (microalgae-bacteria) production, providing a simple technology feasible to be applied in developing countries.

Kinetics of anaerobic degradation of screened dairy manure by upflow fixed bed digesters: Effect of natural zeolite addition

The effect of the hydraulic retention time (HRT) on the performance of two up-flow anaerobic fixed bed digesters (UFAFBDs) packed with waste tire rubber (D1) and waste tire rubber and zeolite (D2) as micro-organism immobilization supports was studied. It was found that a first-order kinetic model described well the experimental results obtained. The kinetic constants for COD, BOD5, total solids (TS) and volatile solids (VS) removal were determined to be higher in digester D2 than in digester D1 or control. Specifically, they were 0.28 ± 0.01, 0.32 ± 0.02, 0.16 ± 0.01 and 0.24 ± 0.01 d− 1 respectively for D1 and 0.33 ± 0.02, 0.40 ± 0.02, 0.21 ± 0.01 and 0.28 ± 0.01 d− 1 respectively for D2. This was significant at the 95% confidence level. In addition, the first-order model was also adequate for assessing the effect of the HRT on the removal efficiency and methane production. Maximum methane yield and the first-order constant for methane production were determined and the results obtained were comparable with those obtained by other authors but operating at higher HRTs. Maximum methane yields and the kinetic constant for methane production were 11.1% and 29.4% higher in digester D2 than in D1.

A comparative study of sand and natural zeolite as filtering media in tertiary treatment of wastewaters from tourist areas

Abstract Anaerobic effluents from a fixed bed reactor treating sewage water from tourist areas were treated by two high rate filters at laboratory scale one packed with sand and the other with natural zeolite with the aim of obtaining final effluents with quality for irrigation of land or disposal in tourist zones. The ranges of particle sizes for the two filtering media used were: 1–3 mm and 0.6–2.5 mm for both media and particle sizes of 0.35–1 mm also for the zeolite. The evaluation of different particle sizes demonstrated that the particle range of 1–3 mm for both media was more effective than the rest of size ranges studied in the removal of pollutant particles. It was found that turbidity removal was similar for sand and zeolite although the filter packed with zeolite had lower pressure losses and better hydraulic behaviour. A maximum ammonia nitrogen removal of 95% was obtained in the first hour of filtration for zeolite medium, although the removal decreased progressively achieving a minimum value...

Evaluation of the quality of the water in El Hondo natural park located in the east of Spain

The purpose of the present work was to evaluate the quality of the water in El Hondo Park, an important wetland located in the east of Spain (province of Alicante) and included on the Ramsar List. The influence of the input of pollutants was assessed over a 14-month period in order to propose remedial action. Three different sources of waters were studied: irrigation water, brackish water and reservoir water. The irrigation water was found to have a high value of conductivity with high concentrations of Cl−, SO4 2 −, Na+ and K+ due to the influence of the brackish water. The concentration of organic matter given as COD T (total chemical oxygen demand) was found to be in the range of 70–600 mg/L of CODT, which was comparable to low-middle strength wastewater. A high concentration of Chlorophyll (a) was found in samples of reservoir water and the eutrophication of this water was thus observed. A high linear relationship was found among CODT, CODF (filtered COD) and BOD5; among electrical conductivity (E.C.), Cl−, SO4 −2, Na+, K+, Ca2+ and Mg2+ and among pH, CO3H− and CO3 2− in all the samples evaluated. Taking this fact into consideration, a simplified water quality index (WQI) was calculated. Using this parameter, the quality of the water from different sources and its variation during the period evaluated was determined to be at a maximum during the months of December to February, which coincided with the period of high precipitations and low temperature. The highest values of this parameter were found in the samples corresponding to the reservoir water while the lowest values were found in the samples of the brackish water. By determination of the WQI, the influence of the brackish water on the quality of water for irrigation and reservoir waters was confirmed.

Treatment of wastewater from red and tropical fruit wine production by zeolite anaerobic fluidized bed reactor

A study of the anaerobic treatment of wastewaters derived from red (RWWW) and tropical fruit wine (TFWWW) production was carried out in four laboratory-scale fluidized bed reactors with natural zeolite as bacterial support. These reactors operated at mesophilic temperature (35°C). Reactors R1 and R2 contained Chilean natural zeolite, while reactors R3 and R4 used Cuban natural zeolite as microorganism support. In addition, reactors R1 and R3 processed RWWW, while reactors R2 and R4 used TFWWW as substrate. The biomass concentration attached to zeolites in the four reactors studied was found to be in the range of 44–46 g volatile solids (VS)/L after 90 days of operation time. Both types of zeolites can be used indistinctly in the fluidized bed reactors achieving more than 80%–86% chemical oxygen demand (COD) removals for organic loading rates (OLR) of up to at least 20 g COD/L d. pH values remained within the optimal range for anaerobic microorganisms for OLR values of up to 20 and 22 g COD/L d for RWWW and TFWWW, respectively. Toxicity and inhibition levels were observed at an OLR of 20 g COD/L d in reactors R1 and R3 while processing RWWW, whereas the aforementioned inhibitory phenomena were not observed at an OLR of 24 g COD/L d in R2 and R4, treating TFWWW as a consequence of the lower phenolic compound content present in this substrate. The volatile fatty acid (VFA) levels were always lower in reactors processing TFWWW (R2 and R4) and these values (< 400 mg/L, as acetic acid) were lower than the suggested limits for digester failure. The specific methanogenic activity (SMA) was twice as high in reactors R2 and R4 than in R1 and R3 after 120 days of operation when all reactors operated at an OLR of 20 g COD/L d.

Piggery waste treatment by using down-flow anaerobic fixed bed reactors

A study of the role of the depth in the performance of laboratory-scale down-flow anaerobic fixed-bed reactors (DFAFBR) was carried out at different nominal hydraulic retention times (HRT N ) using piggery waste as substrate at different influent concentrations (2, 4, 6 and 8 g COD/L). The profiles of soluble chemical oxygen demand (COD) (SCOD), organic nitrogen (O.N.), ammonia nitrogen (A.N.), pH and electrical conductivity (E.C.) through the reactor depths showed an initial highly active zone, which was located around the first half of the reactor depth, and a second zone with a lower biological activity. It was found that the depth of the active zone decreased as the HRT N increased and that the slopes of the profiles obtained increased with the rise in the influent concentration. A hydraulic test showed an increase in the dispersion number when the HRT N increased. The reactors showed a hydraulic pattern between plug-flow and back-mix. The real values of HRT (Θ) also defined as real contact times were determined to be 0.7, 2.1, 3.4, 4.7, 6.4 and 8 days for values of HRT N of 1, 2, 3, 4, 5 and 6 days, respectively. It was found that the concentration of SCOD within the reactor decreased exponentially with the increase in the value of θ. Additionally, the influent concentration had a strong influence on the SCOD variation concentration, mainly at values of θ under 1.5 days, which corresponded to the first part of the reactors.

Effect of a hydrolytic/acidogenic pre-stage on the organic matter content of wastewater treated in a sequencing batch reactor for biological phosphorous removal.

An increase of 52.7% in acetate concentration was observed when urban wastewater was used to feed a pilot-scale upflow-type, fixed-bed fermentor under a hydraulic retention time of 0.78 h. The fermentor influent and effluent were successively used to feed a laboratory-scale sequencing batch reactor (SBR) using similar operational variables of wastewater volume, sludge purging volume and retention times during the anaerobic and aerobic phase, giving a nominal 4 h hydraulic retention time. The fermentor effluent contained an organic substrate, with a volatile fatty acid content higher than 50 mg L−1, which was appropriate for the growth of the type of microorganisms characteristically found in biological phosphorous removal (BPR) systems, and showed the behaviour of an easily and rapidly biodegradable wastewater. The specific rate of phosphorous release at the anaerobic stage was found to be higher than 0.04 mg P r g VSS−1 min−1, when the fermentor effluent is used as feed of the SBR, which demonstrated its favourable conditions for an efficient processing in this type of systems.

The influence of wastewater type and organic loading on the protozoan and metazoan population of a peat bed filter

Three peat bed filters treating wastewaters with differing proportions of industrial input were compared experimentally by analysis of their population strucrure. The plants were all full scale and served village communities around Madrid, Spain. AH three plants showed a high ciliated protozoan population density (> 105/1), but the least loaded system, which received only domestic wastewater, exhibited a 10 fold greater abundance and a predominance of Paramecium. The plants with an industrial input performed less well and showed a population structure predominated by Chilodonella and Colpidium as well as having substantial populations of nematodes and rotifers. Protozoans may contribute towards an enhanced BOD and COD removal efficiency and can be used as indicators of optimum oxygenation conditions with the peat bed.