D. Sales Márquez

Evolution of an activated sludge system under starvation conditions

In this work, the evolution of several physical-chemical and microbiological variables in starvation conditions of an activated sludge are studied. An activated sludge pilot plant was used to study starvation condition effect on biomass. The experiment was studied over a 21-day period, during which no organic material was added to the system. Suspended solids, volatile suspended solids (VSS), pH, dissolved chemical oxygen demand (CODd), dissolved organic carbon (DOC), oxygen uptake rate (OUR), specific oxygen uptake rate (SOUR), identification of microorganisms and total and active cells counting were all monitored. At last of the experiment, an important decrease in the reactor biomass was observed, which may be related both to: the intracellular component degradation from endogenous metabolism, and to the solid depletion occurred, specially, over the first 4 days. Sludge degradation throughout the experiment led to a decrease in the respiratory and enzymatic activity of the microorganisms of the system. During identification tests, some of the typical microbial groups, usually found in an activated sludge, had disappeared and others opportunists appeared. Sludge flocculation capacity decreased with microbial activity diminution and/or microorganism death. From the results obtained, it may be deduced that significant biomass reduction is achieved in first days, specifically, the first one. The highest solid decrease is produced during the first day. Thus, may be interesting to use with an activated sludge system a starvation period of 24 h before stabilization. This can suppose operation and economic benefits.

Start-up of thermophilic-dry anaerobic digestion of OFMSW using adapted modified SEBAC inoculum.

The work presented here concerns the start-up and stabilization stages of a Continuous Stirred Tank Reactor (CSTR) semicontinuously fed for the treatment of the Organic Fraction of Municipal Solid Waste (OFMSW) through anaerobic digestion at thermophilic temperature range (55 degrees C) and dry conditions (30% Total Solids). The procedure reported involves two novel aspects with respect to other start-up and stabilization protocols reported in the literature. The novel aspects concern the adaptation of the inoculum to both the operating conditions (thermophilic and dry) and to the type of waste by employing a modified SEBAC (Sequential Batch Anaerobic Composting) system and, secondly, the direct start-up of the process in a thermophilic temperature regime and feeding of the system from the first day of operation. In this way a significant reduction in the start-up time and stabilization is achieved i.e. 110 days in comparison to 250 days for the processes reported by other authors for the same type of waste and digester. The system presents suitable operational conditions to stabilize the reactor at SRT of 35 days, with a maximum biogas production of 1.944 LR/L.d with a CH(4) and CO(2) percentage of 25.27% and 68.15%, respectively.

Sublethal and lethal toxicity in juvenile Senegal sole (Solea senegalensis) exposed to copper : A preliminary toxicity range-finding test

Static bioassay test for acute toxicity of copper in Senegal sole juveniles (Solea senegalensis) was conducted. The 96h LC(50) value of metal was found to be 0.32mg/L Cu. The intensity of histological alterations was increased gradually with the copper concentration and the exposure time. Numerous aneurysms, hypertrophy, hyperplasia and fusion of the lamellar epithelium in gills and a disorganization of the hepatic parenchyma and vacuolization in liver were common lesions in S. senegalensis juveniles exposed to copper. The results of the study indicate the sensitivity of juvenile S. senegalensis to copper (II), the persistence of sublethal effects and histology as a tool capable of revealing the sublethal effects of heavy metals on the environment and aquatic biota.

Dry-thermophilic anaerobic digestion of simulated organic fraction of Municipal Solid Waste: Process modeling

Solid retention time (SRT) is a very important operational variable in continuous and semicontinuous waste treatment processes since the organic matter removal efficiency--expressed in terms of percentage of Dissolved Organic Carbon (% DOC) or Volatile Solids (% VS) removed--and the biogas or methane production are closely related with the SRT imposed. Optimum SRT is depending on the waste characteristics and the microorganisms involved in the process and, hence, it should be determined specifically in each case. In this work a series of experiments were carried out to determine the effect of SRT, from 40 to 8 days, on the performance of the dry (30% Total Solids) thermophilic (55°C) anaerobic digestion of organic fraction of Municipal Solid Wastes (OFMSW) operating at semicontinuous regime of feeding. The experimental results show than 15days is the optimum SRT (the best between all proved) for this process. Besides, data of organic matter concentration and methane production versus SRT have been used to obtain the kinetic parameters of the kinetic model of Romero García (1991): the maximum specific growth rate of the microorganisms (μmax=0.580 days(-1)) and the fraction of substrate non-biodegradable (α=0.268).

New strategy for a suitable fast stabilization of the biomethanization performance.

The start-up strategies for thermophilic anaerobic reactors usually consist of an initial mesophilic stage (35°C), with an approximate duration of 185 days, and a subsequent thermophilic stage (55°C), which normally requires around 60 days to achieve the system stabilizatio. During the first 8–10 days of the mesophilic stage, the reactor is not fed so that the inoculum, which is generally a mesophilic anaerobic sludge, may be adapted to the organic solid waste. Between mesophilic and thermophilic conditions the reactor is still not fed in an effort to prevent possible imbalances in the proces. As a consequence, the start-up and stabilization of the biomethanization performance described in the literature require, at least, around 245 days. In this sense, a new strategy for the start-up and stabilization phases is presented in this study. This approach allows an important reduction in the overall time necessary for these stages in an anaerobic continuous stirred tank reactor (CSTR) operated at thermophilic-dry conditions for treating the organic fraction of the municipal solid waste (OFMSW): 60 days versus 245 days of conventional strategies. The new strategy uses modified SEBAC technology to adapt an inoculum to the OFMSW and the operational conditions prior to seeding the CSTR.

Inhibitory effects of non-ionic surfactants on the microbial activity of activated sludge system

The purpose of the present work was to study the influence of a non-ionic surfactant, a nonylphenol with four ethoxylated units (NP4EO), on the activity of the microbial population present in a laboratory-scale activated sludge unit. Traditional control methods for this type of unit were used (measurement of suspended solids and chemical oxygen demand) as well as specific techniques for the measurement of bacterial activity (dehydrogenase activity and specific oxygen uptake rate) and the results were compared. It was shown that the Specific Oxygen Uptake Rate (SOUR) is the simplest and quickest way to carry out routine control of activated sludge activity, while measuring dehydrogenase activity provides more complete control. The results obtained indicated that there was no inhibition of microbial activity at a concentration of 5 ppm of NP4EO, which was not the case with a concentration of 10 ppm.

Influence Of The Inouculum Percentage In Thermophilic Anaerobic Biodegradation Assays Of Oily Wastewater

The wastes with a high content of fatty and oily matter, derived from industrial process, have a high level of heavy metal, microorganisms, decomposition products, etc. So, they are considered like danger wastes by the legislation in force (Law 10/1998, of 21 of April) [1] and must be treated properly to eliminate determine components before their thrown to urban collectors or any other final channels. The objective of this work has been to study the influence of inouculum percentage in thermophilic anaerobic biodegradation assays of the wastes generated fi-om a high installation dedicates to the mechanizing of metallic pieces for the automotive sector; thus, to select suitable analytical and operative methodology to the following and control of the degradation process values. The experimental results obtained show that the composition of inouculum medium has a real effect on the behaviour of the system. So, it is noticeable that there is a direct proportion between the evolution of analysed parameters and the inouculum amount added to the assay medium. All of these factors advise about the modification of the inouculum process, and it is proposed the inouculum centrifugation to separate solid fi-actionand resuspend it in an equivalent amount of waste before its addition to the assay; in this way, the biodegradability matter goes with the inouculum is almost deleted. On the other hand, the values of output coefficient of methane show how the elimination of organic matter and its transformation in methane has a higher correlation with the TOC and DVS than the COD, due to the nature of the waste used.